Preheat the oven to 175 degrees Celsius.
Combine the dry ingredients for the brownie in a bowl.
Whisk together the egg and granulated sugar in a separate bowl.
Add stevia drops, yogurt/quark, apple sauce, and milk and stir until combined.
Fold in the dry ingredients and stir just until combined.
Pour the brownie batter into a lined baking pan or into silicone bar molds.
Bake in the oven for 16-18 minutes in the baking pan or 13-16 minutes in the silicone molds.
Take out and let it cool.
Mix the ingredients for the hazelnut ice cream in a high speed blender (except for the chopped hazelnuts). Taste to check if more sweetener or hazelnut butter is needed. Stir in the chopped hazelnuts.
Add the hazelnut ice cream on top of the brownie (keep the brownie in the mold/baking pan). Freeze for a few hours.
Melt chocolate in a microwave or over a water bath.
If you baked the brownie in a baking pan slice it up into slices/pieces.
Now either dip the whole brownie/hazelnut bar un the chocolate or just cover the top and the sides. Sprinkle with sea salt, hazelnuts, any other topping or skip the topping.
Store in the freezer, take out five minutes before eating.