Layered cake with apple jam filling and sugar grape topping

Ingredients:

Cake

• 3 and 3/4 cups premium flour, plus extra for dusting the pans
• 3/4 teaspoon baking soda
• 0.5 tsp salt
• 2 and 1/4 cups granulated sugar
• 1 cup vegetable oil
• 4 large eggs, room temperature
• 2 tsp vanilla extract
• 1.5 tbsp. sour milk
• Butter for greasing the pans

Interlayer

• 4 cups seedless grapes (about 900 g), such as Concord
• 1 small Granny Smith apple, peeled and finely diced
• 0.5 cups of water
• 1 cup granulated sugar

Decoration

• 2 pasteurized large egg whites
• 1 cup granulated sugar
• 1 cup medium seedless Concord grapes (about 220 g)
• 350 g butter, room temperature
• A pinch of salt
• 4 cups sifted powdered sugar
• 2 tsp vanilla extract

Preparation:

1. Prepare the layerCombine the grapes, apple, and water in a medium saucepan over medium-low heat. Cover and simmer until most of the grapes have burst and shriveled, about 12 minutes. Increase the heat to medium and stir in the granulated sugar.
   
   Cook, stirring frequently and occasionally mashing the apples with a potato masher, until the filling is thick and syrupy, 15-20 minutes. Remove from the heat and cool completely.
2. Preheat oven to 175°C. Grease and flour three 20cm round cake pans. Line the bottoms with parchment paper.
3. Bake the cakesIn a medium bowl, sift the flour, baking soda, and salt. In a large bowl, beat the sugar and vegetable oil with a mixer on medium-high speed until the mixture resembles wet sand, about 2 minutes.
   
   Scrape down the sides of the bowl and add the eggs one at a time, beating well after each addition. Add the vanilla; beat on high speed until light and fluffy, about 2 minutes. Reduce mixer speed to low; beat in the flour mixture in 3 additions, alternating with the buttermilk, beginning and ending with the flour. Continue beating until smooth, about 1 minute.
4. Pour the batter evenly into the prepared pans and bake until a toothpick inserted into the center comes out clean, 25-30 minutes. Let cool in the pans for 10 minutes, then turn out onto a wire rack, remove the parchment paper, and cool completely.
5. Meanwhile, make the topping.Line a baking sheet with parchment paper. Whisk the egg whites in a medium bowl until foamy. Spread the sugar in a pie plate or shallow bowl. Dip the grapes in the egg whites, let any excess drip off, and then roll the grapes in the sugar. Place the candied grapes on the prepared baking sheet and freeze for at least 30 minutes.
6. Prepare the butter creamIn a large bowl, beat the butter and salt with a mixer on medium speed until smooth, about 2 minutes. Gradually beat in the powdered sugar, then the vanilla. Increase the mixer speed to medium-high and beat until very light and fluffy, about 2 more minutes.
7. Assemble the cakePlace one cake layer on a cake stand or plate. Spread about a third of the grape-apple filling on top, then top with another cake layer and half of the remaining filling. Top with a third cake layer. Frost the top and sides of the cake with buttercream.
   
   Refrigerate the cake for 15-20 minutes to allow the filling to soak into the cake and the frosting to set. Spread the remaining filling over the top of the cake, leaving a 1 cm border around the edges. Arrange frozen grapes around the edge of the cake, leaving the filling exposed.