Preheat the oven to 300°F/ 150°C. Lightly grease the mold you will use with a little butter.
Melt the remaining butter in the microwave. Then, in a mixing bowl, add the wet ingredients: milk, eggs, vanilla, and melted butter. Beat very well with a hand mixer until they are fully integrated.
Add sweetener to the mix, stir, and make sure there are no lumps.
In another bowl, sift almond flour with baking powder and grated lemon rind.
Add the sifted flour mix to the bowl, little by a little, while stirring until you get a mixture of thick consistency, similar to the cake mix.
Pour the mixture carefully into a silicone mold, and bake it in the oven for about 30 minutes.
When waffles turn brown on top, remove from oven, unmold and serve with sour cream and some fresh berries.