I was asked to share the recipe, so here it is.
It is also a good activity with kids.
3/4 cup of rice flour.
1/3 cup of cocoa.
2 tbsp, or more, of sweetener, honey, maple syrup.
1 unsalted butter bar.
1 tbsp of vanilla.
1 pinch of salt.
Let the butter soften at room temperature. Then mix all the ingredients with your hands in a bowl.
Preheat the oven at 350º F.
Make a roll and cover it with wax paper, freeze it for 30 minutes.
Cut slices of 1/4 inch and bake for 15 minutes.
To give them the heart shape you just press one side of the roll on the over the wax paper and then press a knife on the other side.