Rhubarb Custard Cake Recipe

I can’t wait for you to see the glossy custard and ruby ribbons of rhubarb that make this cake the single most irresistible dessert you’ll save for serious sweet cravings.

I am obsessed with this Rhubarb Custard Cake because the tartness of chopped rhubarb cuts through a lush custard and I can’t get over that contrast. I love how vanilla extract threads through the custard, subtle but insistently there.

My friends always ask for more at parties; truth is I’m secretly thrilled when they devour it. I crave the bright, tangy fruit, custard, streusel on top.

I find it the kind of dessert that wrecks your willpower. I mean about the food.

And yes, I linger over the last bite. I plan to make it each spring until people beg.

Ingredients

• Flour: Gives structure and that cakey crumb you’ll slice and love.
• Baking powder: Basically makes it light and airy, so it’s not dense.
• Salt: Balances sweetness and wakes up the other flavors.
• Granulated sugar: Sweetness and that tender crumb you expect.
• Butter: It’s richness and flavor, plus a softer bite.
• Eggs: Hold everything together and add a little protein.
• Vanilla: Adds warmth and rounds out the sweet notes.
• Milk: Keeps the batter moist and silky.
• Sour cream: Plus tang and extra moistness, kind of creamy.
• Rhubarb: Tart, juicy pockets that cut through the sweetness.
• Custard eggs: Create a creamy custard layer, smooth and custardy.
• Custard sugar: Sweetens that custard so it’s not bland.
• Cornstarch: Thickens the custard, so it sets nicely.
• Custard milk: Makes the custard lush and drinkably smooth.
• Custard vanilla: Basically more depth and a comforting scent.
• Brown sugar streusel: Adds caramel notes and chew to the topping.
• Streusel flour: Gives the crumble some heft and holds it together.
• Streusel butter: Cold cubes make that flaky streusel crunch.
• Cinnamon: Optional warmth, pairs nicely with tart rhubarb.
• Pinch of salt: Just a little boost for all the sweetness.
• Nuts: Plus crunch and nuttiness, totally optional but tasty.

Ingredient Quantities

• 1 1/2 cups all purpose flour
• 1 tsp baking powder
• 1/4 tsp salt
• 1 cup granulated sugar
• 1/2 cup unsalted butter, softened
• 2 large eggs, room temperature
• 1 tsp vanilla extract
• 1/2 cup whole milk
• 1/2 cup sour cream or plain yogurt
• 3 to 4 cups chopped rhubarb (about 1 to 1 1/4 lb), trimmed
• 3 large eggs for the custard layer
• 3/4 cup granulated sugar for the custard
• 1/4 cup cornstarch
• 1 1/2 cups whole milk for the custard
• 1 tsp vanilla extract for the custard
• 1/2 cup packed light brown sugar for streusel
• 1/2 cup all purpose flour for streusel
• 1/4 cup cold unsalted butter, cubed for streusel
• 1/2 tsp ground cinnamon (optional)
• Pinch of salt
• Optional: 1/2 cup sliced almonds or chopped walnuts for topping

How to Make this

1. Preheat oven to 350 F and grease a 9×13 inch pan, line with parchment if you want easier slicing later. Toss the chopped rhubarb with a tablespoon of sugar and set aside so it loses a bit of liquid.

2. Make the cake batter: whisk together 1 1/2 cups flour, 1 tsp baking powder and 1/4 tsp salt in a bowl. In another bowl cream 1/2 cup softened butter with 1 cup sugar until light, then beat in 2 large eggs one at a time, add 1 tsp vanilla, 1/2 cup whole milk and 1/2 cup sour cream or plain yogurt until just combined. Fold the dry ingredients into the wet until mostly smooth, dont overmix.

3. Spread the batter into the prepared pan in an even layer, smooth the top with a spatula. Press down a little so it will hold the custard and rhubarb.

4. Make the custard: whisk together 3 large eggs and 3/4 cup sugar until pale. In a small bowl mix 1/4 cup cornstarch with a little of the 1 1/2 cups whole milk to make a slurry, then whisk that into the eggs. Add the rest of the milk and 1 tsp vanilla and whisk until smooth. Strain if you want extra silky custard.

5. Carefully pour the custard over the cake batter. It will seem thin but it will set while baking. Scatter the macerated rhubarb evenly over the custard. The rhubarb may sink a little which is fine.

6. Make the streusel: rub together 1/2 cup packed light brown sugar, 1/2 cup flour, 1/4 cup cold cubed butter, 1/2 tsp cinnamon if using and a pinch of salt until it looks like coarse crumbs. You can pulse briefly in a food processor too. Stir in 1/2 cup sliced almonds or chopped walnuts if you want extra crunch.

7. Sprinkle the streusel evenly over the rhubarb and custard, press lightly in places so it sticks. If you like extra nuts save a few to sprinkle on top after baking.

8. Bake at 350 F for about 50 to 60 minutes, rotating once if your oven runs hot, until the custard is set in the middle and the streusel is golden. A thin knife inserted in the center should come out mostly clean with a few moist crumbs, not runny custard.

9. Let the cake cool completely in the pan on a wire rack, at least 1 to 2 hours so the custard finishes setting. Refrigerate for a firmer slice if you prefer, especially in warm weather.

10. Slice and serve chilled or at room temp, top with reserved nuts if you like. Leftovers keep covered in the fridge for 3 to 4 days and actually taste better a day later after the flavors settle.

Equipment Needed

1. Oven (preheat to 350 F)
2. 9×13 inch baking pan (parchment optional for easier slicing)
3. Mixing bowls (one large for dry, one medium for wet, one small for cornstarch slurry)
4. Electric mixer or sturdy wooden spoon for creaming the butter and sugar
5. Whisk (for eggs, custard and slurry)
6. Silicone spatula (to spread batter and scrape bowls)
7. Chef knife and cutting board (for chopping rhubarb)
8. Fine mesh sieve (optional, for a silky custard)
9. Measuring cups and spoons
10. Wire cooling rack (let cake cool and set)

FAQ

Rhubarb Custard Cake Recipe Substitutions and Variations

• All purpose flour:
  • Whole wheat pastry flour, use 1:1 for a nuttier flavor, cake will be a bit denser
  • 1:1 gluten free baking blend, use same amount, add 1/4 tsp xanthan gum if blend lacks it
• Unsalted butter (softened):
  • Coconut oil, solid at room temp, use same volume, gives a slight coconut note
  • Margarine or vegan butter, use same amount, works well for texture if dairy-free
• Sour cream or plain yogurt:
  • Buttermilk, use 1/3 cup buttermilk plus 1/6 cup milk to equal 1/2 cup, keeps tang and moisture
  • Crème fraîche, swap 1:1 for richer, silkier custard
• Chopped rhubarb:
  • Frozen rhubarb, thaw and drain excess liquid, use same weight
  • Tart apples (Granny Smith) or sour cherries, chop and toss with 1 tbsp sugar to mimic rhubarb tartness

Pro Tips

1. Chill the rhubarb after you toss it with sugar for 10 to 20 minutes, then drain off most of the liquid before adding it to the custard. Too much free liquid will water down the custard and make the streusel soggy, so pat the pieces lightly with a paper towel if they seem too wet.

2. Warm the milk for the custard to just below simmering before whisking it into the eggs and cornstarch slurry. That helps the custard thicken more evenly and reduces the chance of grainy spots. If you see any lumps, strain the custard through a fine sieve for a silky finish.

3. Make the streusel with very cold butter and don’t pulverize it. You want pea sized butter bits so the topping bakes up with crisp, buttery pockets. If using a food processor pulse only a few times, or use your fingers to rub the butter in.

4. Let the pan cool fully, at least an hour, then refrigerate for another hour if you want clean slices. The custard firms as it chills and slices neater after resting. If you need to speed things up, run a thin knife around the edges and chill the cake uncovered for 30 minutes to reduce condensation.