Alfajores

Steps

1. mix4 min
   medium speed
   Cream the softened butter and sugar until smooth and slightly lighter, then mix in the eggs, vanilla, and lemon zest. Stop once homogeneous; excessive aeration makes these tender cookies puff and distort instead of staying flat enough to sandwich.
2. mix3 min
   low speed or by hand
   Whisk flour, cornstarch, baking powder, and salt separately, then fold them into the butter mixture just until no dry pockets remain. The high cornstarch dough is intentionally fragile; overmixing develops wheat gluten and works against the short, tender crumb.
3. prep30 min
   refrigerated, wrapped
   Flatten the dough into a disc and chill until firm enough to roll without cracking or sticking. The chill is for handling, not for making the dough hard; if it becomes rigid, let it stand a few minutes before rolling.
4. prep10 min
   3 to 5 mm thick
   Roll the dough gently and cut 4-to-5-centimeter rounds, transferring them to a lined tray with a little space between each. Re-roll scraps once; repeated working toughens the flour portion and makes later cookies less delicate.
5. bake8 min
   175 C / 350 F, just set and still pale
   Bake until the surfaces are dry and the bottoms are only barely colored. Browning is not the goal: a golden cookie is already moving away from the soft, pale maicena texture supported across the Argentine sources.
6. prep15 min
   cool completely
   Cool the cookies before filling. Warm cookies melt the dulce de leche and make the sandwiches slide, while fully cooled discs stay crisp enough to handle yet tender when eaten.
7. top5 min
   gentle pressure
   Spread a generous spoonful of firm dulce de leche on half the cookies, cap with the remaining discs, and press only until the filling reaches the edge. Roll the exposed filling in coconut if using; pressing hard enough to squeeze filling out will crack the fragile cookies.