Preheat your oven to 220°C (410°F). Grease your baking molds with butter. (Silicone molds do not need to be greased.)
In a bowl, combine all the dry ingredients: almond flour, all-purpose flour, sifted, powdered sugar, sifted, and baking powder. Mix well.
Add wet ingredients: 6 egg whites and liquid vanilla extract (or 1 packet vanilla sugar) to the dry mixture. Mix together using a hand mixer until combined.
Add unsalted melted butter, and mix well. The batter will be fairly runny — this is normal.
Pour the batter into the prepared molds. Sprinkle with 1 tablespoons sliced almonds (optional, for topping) if desired.
Bake in the preheated oven for approximately 20 minutes , until golden brown.
Baking time may vary depending on your oven and the size of your molds.