1. Preheat the oven to 350F.2. In a bowl, add the melted butter, sugar, eggs, and vanilla.3. Gradually add the flour mixed with baking powder and salt.4. Finish with the chocolate and mix well but not too long.5. Using a spoon, place the dough on a baking sheet lined with parchment paper. Bake for 8 minutes. Remove from the oven and let cool on a rack.6. To make the mousse, heat the cream over low heat in a small non-stick saucepan.7. Incorporate the white chocolate pieces, one by one. Make sure the mixture is smooth and homogeneous. Remove the saucepan from the heat, let it cool, then refrigerate for 2 hours.8. Remove the cream from the refrigerator, then whip it with an electric beater. Assemble the white chocolate mousse on half of the cookies and cover with another cookie. Refrigerate for an additional 30 minutes before serving.