Preheat oven to 320° F.
In a mixer, mix together the butter.
If you're dyeing the cookies, now would be the best time, to prevent streaking.
Also add the ginger powder and vanilla paste. Mix in well.
Zest half a lemon into dyed butter. Add egg yolks. Mix well.
Add baking powder, salt, baking soda and powdered sugar and mix very well.
Mix in the cornstarch and flour. If by hand, you may need to knead this in. This dough borders on dry.
Roll dough. If you're in a hot climate, refrigerate for 30 minutes, covered with plastic wrap before rolling. Don't add more flour to roll, as this dough again is quite dry. Roll between parchment or in plastic wrap, if needed.
Cut to your preferred shape and size. In this case a heart, 1.5" size.
Place in oven for about 16 minutes. Cookie should release from pan's parchment easily. Cool before removing cookies and filling them.
Match two cookie shell together to match for the sandwiches.
Add dulce de leche to piping bag. Cut edge to decent size opening. Pipe adjacent connected lines in a downward motion to fill the hearts. Try not to overfill. Cover filled shell with top shell.
Decorate of desired.