Beat the butter, sugar, and zest (or cinnamon) until light and fluffy, about 3 minutes. Add the yolk and vanilla and beat until combined.

Whisk together the flour, almond flour, and salt. Add to the egg mixture and mix until just combined.

Divide the dough in half, pat each into a disc, wrap in plastic wrap, and refrigerate until firm, about 1 hour.

Remove the dough from the refrigerator, soften for 5-10 minutes, then roll out about ⅛" thick. Cut out cookies and transfer to a baking sheet.

Cut 15 rounds from the remaining dough and create a peekaboo cutout in the center of each. Chill both trays for 30 minutes.

Preheat the oven to 350°F while the cookies are chilling.

Bake cookies for 12-15 minutes, until edges are just turning brown. Cool for 5 minutes, then transfer to a rack.

Sift confectioners' sugar over the cookies with holes. Spoon ½ teaspoon of jam or lemon curd onto the flat side of the remaining cookies and top with the sugar-dusted cookies.

Store filled cookies at room temperature (if filled with jam) or in the refrigerator (if filled with curd) for several days; freeze for longer storage.