Preheat oven to 350 degrees F. Grease a 9-inch cake pan.

Combine cherries with amaretto and 1 tablespoon sugar, stirring to combine. Let sit for 30 minutes. Drain cherries, reserving liquid.

Mix together 2 tablespoons melted butter with ½ cup brown sugar. Spread mixture in bottom of cake pan in an even layer. Arrange cherry halves on top, cut sides facing down. Gently press down on cherries into sugar mixture.

Make cake batter. Combine flour with hazelnut flour, baking powder, baking soda, and salt in a medium bowl. Set aside.

Beat together butter with sugar in the bowl of a stand mixer until light and fluffy, about 3 minutes. Add eggs one at a time, fully incorporating the egg before adding the next. Add vanilla and stir to combine.

Add half of flour mixture, stirring just until combined. Add buttermilk, then remaining flour mixture stirring just until combined. Pour cake batter on top of cherries, spreading it out into an even layer. Bake cake for 45-50 minutes or until a toothpick inserted in the center comes out clean.

Remove cake from oven and let cool 20 minutes. Use an offset spatula or knife to loosen edges of cake. Place a plate on top and carefully invert cake. Let cool completely.

Whip heavy cream with powdered sugar until stiff peaks form. Add 3 tablespoons reserved amaretto syrup and whip for another minute. Slice cake and serve with amaretto whipped cream.