Measure almond flour, confectioners' sugar and cocoa powder into the food processor. Pulse a few times to mix. Grind to fine powder, letting processor run, 1 full minute.
Beat together egg whites and lemon juice, using an electric mixer with a whisk attachment. Gradually pour in granulated sugar. Continue beating, past frothy, past glossy, past soft peaks, all the way to sturdy peaks, about 5 minutes.
Scatter half the almond mixture over egg whites. Gently fold in with a spatula. Scatter on remaining almond mixture. Fold in.
Scrape into a pastry bag with a plain tip or a plastic bag (snip off 1 corner). Pipe 1-inch circles onto a buttered parchment-lined baking sheet (use an air-cushioned sheet or two stacked up).
Slide into a 300-degree oven. Bake until tops turn dry to the touch and cookies are still soft, 8-10 minutes. Cool on pan a few minutes before transferring to a cooling rack.
Flip half the cooled cookies flat-side up. Pipe or spread on a layer of filling. Top with remaining cookies, forming sandwiches. Settle in an airtight container and chill overnight, if you can. Bring to room temperature. Enjoy.
Combine 1 cup almond flour, 1/2 cup sugar, 4 tablespoons softened unsalted butter, 1 teaspoon vanilla and a pinch flaky salt. Thin with 1 tablespoon cold espresso.
Leah Eskin is a Tribune special contributor e-mail her at firstname.lastname@example.org