Preheat the oven to 325°F. Grease an 8 x 8–inch pan with a nonstick cooking spray and then line the pan with parchment paper, leaving the sides to overhang the edges.

Melt the butter and pour over the chopped chocolate. Cover for 2 minutes and stir until it melts completely.

Combine the eggs, both sugars, salt, vanilla, and instant espresso in the bowl. Whip on medium-high until extremely thick and fluffy, about 5 minutes.

In the meantime combine gluten-free flour, cocoa powder, and baking powder. Also now is the time to stir together your melted butter-chocolate mixture.

When your egg-sugar mixture looks fluffy and thick, slow down the speed of your mixer to low and add the chocolate-butter mixture. Mix until combined.

Once the egg-sugar mixture and the butter-chocolate mixture are combined, turn the speed of your mixer to SLOW and add cocoa flour all at once. Carefully mix until roughly combined. Turn off the mixer and with a flexible spatula fold in the flour cocoa mixture. Make sure to get the bottom of the pan.

Bake the brownies for 20 minutes at 325F.

Remove the brownies from the oven, top with some flaky sea salt and allow to cool completely.