Generally speaking, I'm not a fan of many gluten-free desserts or snacks. They claim to be healthy by avoiding wheat, but then compensate for the lack of flavor and texture by overloading with bad fats, salt and sugar. This brownie/cake combo is the exception. It's full of great flavor, which make me happy, and is gluten-free thanks to ground hazelnuts, which makes my wife (on a GF diet) happy.
When buying hazelnuts, the most important thing to remember is that the nuts are raw and of the best quality you can find. No surprise: Amazon is a great source for that.
9 oz. ground hazelnuts
5 1/2 oz. (2/3 cup) sugar
4 oz. (1 stick) unsalted butter
1 oz. cocoa powder
1 tablespoon baking powder
Pour the hazelnuts into a food processor and grind them as fine as you can. It won't be powdery, like flour, but like tiny particles. Dump them into a separate bowl.
Back in the food processor bowl, add the sugar and butter and pulse until combined. Crack the eggs in a separate bowl, and add them slowly to the sugar and butter, pulsing to mix in between each addition.
Pour the ground hazelnuts into the mixture a little at a time, pulsing after each addition. Add the cocoa powder and baking powder, straining them through a sieve to keep out lumps, and pulse again. Scrape down the sides of the bowl and give it all one last mix.
Pour the batter into a buttered pan and cook at 350 for 30 minutes. Use a deeper pan so that the brownies don't overflow as they rise while baking.