• In a separate bowl carefully mix together the flour, corn starch, and baking soda. Corn starch is one of those things you'll be finding for days if you're too aggressive. Sift if you see fit.
• In a large bowl or with a stand mixer, mix butter and sugar until creamy, 2-3 minutes
• Add egg yolks and egg and mix well.
• Add brandy/cognac, vanilla, and lemon zest and mix well.
• With the mixer running, gradually add the flour mixture a tablespoon or two at a time until it's all added and there are no dry streaks remaining. The final dough will be silky, not sticky.
• Let rest for 10-20 minutes.
• Heat oven to 325°F / 170°C
• On a floured surface roll dough to ¼-inch / 5mm thick.
• Prepare a couple of sheet pans with cooking spray, butter, Silkpat, or parchment AND cooking spray. For being such an unsticky dough these stick when baked.
• Using a small round cutter cut circles and place on a prepared sheet pan.
• Bake for 10-12 minutes or until just starting to color.
• Remove from oven and let cool for 5-10 minutes before removing to cooling rack to cool completely.

Filling And Coating

• Using either a spoon or a piping back put about 1 tablespoon of Dulce De Leche on the flat side of a cookie. Take another cookie and press Dulce De Leche lightly with the flat side to make a sandwich. The Dulce De Leche should be even and reach to the edges evenly.
• If any Dulce De Leche is leaking out, flatten with the back side of a spoon.
• (Optional) Put the coconut on a plate and roll the sides of the alfajores to coat.