1. Preheat and Prepare the Pans: Set your oven to 350°F (175°C). Line three 10-inch cake pans with parchment paper and spray with non-stick spray. If you don’t have three pans, you can bake the layers in batches.

2. Mix Dry Ingredients: In a medium bowl, sift together the flour, baking powder, and baking soda. Set aside.

3. Beat Eggs and Sugar: In the bowl of a stand mixer or with a handheld mixer, beat the eggs on high speed until light and fluffy (about 5–7 minutes). Gradually add in the sugar and continue beating until the mixture is pale and thickened.

4. Add Sour Cream and Oil: Reduce the mixer speed and gently mix in the sour cream and oil until just incorporated. Avoid overmixing.

5. Fold in Dry Ingredients: Using a whisk or spatula, carefully fold the sifted flour mixture into the egg mixture. Do this gradually to avoid deflating the batter.

6. Divide the Batter: Split the batter evenly into three separate bowls. Add the hazelnuts to one bowl, cherries to another, and poppyseeds to the third. Gently stir each until evenly distributed.

7. Bake the Layers: Pour each flavored batter into its own prepared pan. If your oven can’t accommodate all three at once, bake the cherry and hazelnut layers first as these are heavier and more likely to settle. Bake each layer for 15–18 minutes, or until a toothpick inserted into the center comes out clean.

8. Cool the Cakes: Let each cake layer cool in its pan for 10 minutes, then carefully transfer to a wire rack to cool completely.

9. Prepare the Cream Filling:

• In a large mixing bowl, beat the softened butter with the cooked sweetened condensed milk until smooth and fluffy.
• Add the sour cream and beat until fully incorporated.
• In a separate bowl, whip the heavy cream until stiff peaks form.
• Gently fold the whipped cream and vanilla into the butter mixture. Chill slightly if the frosting is too soft to spread.

10. Assemble the Cake: Place the hazelnut layer on your serving plate and spread a generous layer of cream over it. Follow with the poppyseed layer, more cream, then the cherry layer on top. Finish with a final coat of cream on top and sides, if desired.

Optional Decoration: Decorate with fresh or dried cherries, chopped nuts, or rolled wafer cookies filled with cream. A light dusting of cocoa powder or grated dark chocolate can also add a polished finish.