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Square of white sheet cake topped with cream cheese layer and fruit topping on white plate with fresh blueberries.

Grandma's Famous Sheet Cake

Yield: 20 to 20 servings
Prep Time: 1 hour
Cook Time: 25 minutes
Chilling Time: 2 hours
Total Time: 3 hours 25 minutes

Ingredients

Fruit Topping:

  • 2 ½ cups (365 g, more or less) fresh or frozen fruit, like blueberries, raspberries, blackberries, huckleberries, triple berry blend, etc
  • ¾ cup (177 g) cold water (use 2 to 3 extra tablespoons water if using fresh fruit)
  • ⅓ cup (71 g) granulated sugar
  • 2 ½ tablespoons cornstarch
  • 1 tablespoon fresh lemon juice

Cake:

  • ½ cup (113 g) salted butter, softened to room temperature
  • 1 ⅓ cup (283 g) granulated sugar
  • ⅓ cup (65 g) vegetable oil (or other neutral flavored oil)
  • 4 large (120 g) egg whites, room temperature
  • 1 teaspoon clear or regular vanilla extract
  • 1 ¾ cups (249 g) all-purpose flour
  • 1 tablespoon baking powder
  • ½ teaspoon salt
  • 1 cup (242 g) 2% or whole milk, room temperature
  • ¼ cup (56 g) full fat sour cream, room temperature

Cream Layer:

  • 6 ounces (170 g) cream cheese, softened to room temperature
  • ½ cup (57 g) powdered sugar
  • 1 tablespoon fresh lemon juice
  • ½ teaspoon vanilla extract
  • 2 cups (480 g) chilled heavy whipping cream (see note)

Instructions 

  • For the fruit topping, in a medium saucepan, combine the fruit, cold water, sugar cornstarch, and lemon juice. Stir to combine until the cornstarch is dissolved.
  • Cook over medium heat, stirring often, until the mixture begins to simmer. Continue to cook, stirring constantly, until large bubbles pop at the surface and the mixture has thickened (it will thicken a bit more as it cools).
  • Scrape the mixture into a container with a lid. Cover, and let cool completely. The fruit topping can be made several days in advance and refrigerated.
  • For the cake, preheat oven to 350 degrees F. Position a rack in the middle of the oven. Lightly grease a half sheet pan (about 17X12-inches) with nonstick cooking spray and set aside.
  • In the bowl of a stand mixer fitted with the paddle attachment or in a mixing bowl with a handheld mixer, add the butter, sugar and oil. Mix on low speed until combined. Increase mixer to medium speed and mix for three full minutes, scraping down the sides of the bowl as needed, until the mixture is very light in color. Don't short this step - it's important for a moist, tender cake.
  • Add the room temperature egg white and vanilla and mix until evenly combined.
  • In a separate bowl, whisk together the flour, baking powder and salt.
  • Measure the milk into a liquid measuring cup and add the sour cream. Whisk to combine.
  • Add 1/3 of the flour mixture to the cake batter. Mix on low speed until just combined (a few dry streaks of flour are ok). Add 1/2 of the milk mixture and mix until combined. Add 1/3 of the flour. Mix. Add remaining milk mixture. Mix. Add final addition of flour and mix until just combined and no dry streaks remain.
  • Spread batter evenly in the prepared pan. Bake for 20 to 22 minutes until the center of the cake springs back lightly to the touch. Don't over bake.
  • Remove from the oven and let the cake cool completely in the pan.
  • For the cream layer, in the bowl of a stand mixer fitted with the paddle or whisk attachment or in a mixing bowl with a handheld electric mixer, mix the cream cheese and powdered sugar together until smooth and creamy.
  • Add the vanilla and lemon juice and mix until combined.
  • Add 1 cup heavy cream. Mix until combined. Add remaining heavy cream and mix on low speed until combined. Increase speed to medium and continue mixing until the mixture has thickened to soft peaks. It should be thick, creamy, but still very spreadable (don't over mix).
  • To assemble, spread the cream topping evenly over the cooled cake. Refrigerate the cake for about an hour for the cream layer to firm up a bit (you can skip this step, but it may make the fruit topping harder to spread without swirling the cream layer).
  • Dollop the fruit topping in large spoonfuls across the cream layer. Spread evenly across the cake.
  • Serve immediately or chill the cake for up to 2 hours before serving (any longer and the fruit topping may discolor the cream layer a bit - still tastes great).

Notes

Cake Mix Substitution: A white cake mix can be substituted for the homemade cake mix (the cake layer is a bit thinner using a cake mix). 
Room Temperature Ingredients: Bringing the egg whites, milk, and sour cream to room temperature is important for a super fluffy, moist cake. If I haven't planned ahead, I pop the eggs in a bowl of warm water and let them sit for 5 to 7 minutes and microwave the milk and sour cream for 15 to 20 seconds until no longer chilled.
Fruit: Many different types of fruit can be used for the topping. I grew up eating this with huckleberries, but any sweet-tart fruit will work well. You can adjust the amount of sugar and lemon juice in the fruit topping depending on the sweetness or tartness of the fruit you are using. I usually use frozen fruit, but fresh fruit can be used, as well. As noted in the ingredients list, increase the water by a few tablespoons if using fresh fruit.
Cream: To simplify making the cream layer, the heavy cream can be added directly to the cream cheese mixture without whipping the cream to soft peaks first. This method works if the cream is "heavy" whipping cream with a milkfat percentage of 36 to 40% (regular whipping cream may not work as well this way and may need to be whipped first before folding in the cream cheese mixture).