Preheat the oven to 350F. Line 2 to 3 baking sheets with parchment paper.
In a medium saucepan, melt butter over medium heat. Add the brown sugar, corn syrup, and salt. Stir constantly until the mixture comes to a simmer, about 3 minutes. Remove from the heat.
Stir in the flours and the vanilla. Let the mixture cool for 10 to 15 minutes or until it starts to thicken and is cool enough to handle. Scoop 1 teaspoon of batter and quickly roll into a ball in your palms. Place onto the prepared pans, separating each by about 3 inches. (I bake 5 cookies per baking sheet.) The dough will continue to get firm as it cools which is fine; there's no need to reheat it.
Bake one sheet at a time for 8 to 10 minutes, rotating the pan halfway through baking, or until the cookies have spread very thin and have mostly stopped bubbling. (They should have darkened in color and be only slightly lighter in color at the center than the edge. Let the cookies cool on the baking sheet until firm, 10 to 15 minutes then transfer to a wire rack.
Keep a close eye on the lace cookies as they bake, especially near the end of the baking period. As the cookies are so thin, they’ll burn very quickly if you leave them in the oven for too long.
Use real vanilla extract instead of artificial extract for the best-tasting almond lace cookies.
Use real butter and not margarine, as margarine doesn’t brown and caramelize like real butter.
Make sure to line the baking sheets with just parchment paper. Do not use tin foil or grease your cookie sheet, as the cookies won’t come out thin and lacy.
Be sure to use almond flour instead of almond meal. Almond meal is more coarse and won’t yield the same results.
Use to spatula to help transfer the cookies once cooled for minimum breakage.