1. Preheat the oven to 350°F.
2. In a bowl, beat the butter and sugar for 4 minutes. Add the egg and vanilla; mix.
3. Sift the flour, baking powder, cocoa powder, baking soda, and salt. Add to the preparation.
4. Add the milk, beating slowly.
5. Transfer the preparation to a piping bag with a simple nozzle.
6. On a baking sheet lined with parchment paper, form small heaps of dough, spaced apart. Bake for 10 minutes.
7. Remove from the oven and let cool on a rack.
8. For the cream: beat the eggs with the sugar.
9. Add the lemon juice and cook over a water bath until a lightly thickened cream is obtained. Incorporate the butter.
10. Let cool, stirring occasionally to prevent a skin from forming on the surface of the cream.
11. Fill the cookies with lemon cream and stack them with another.
12. For the glaze: mix the powdered sugar and food coloring, add the water.