Beat the butter and erythritol with an electric mixer until creamy. Add the egg yolk and vanilla. Mix in the almond flour, baking powder and salt until a dough forms. Wrap the dough in cling film and place it in the fridge for an hour.

100 g unsalted butter 40 g erythritol 1 egg yolk 200 g almond flour ½ tsp baking powder salt 55 g unsalted butter 30 g powdered erythritol ¼ tsp salt ½ tsp extra sea salt