Preheat oven: Set to 325F (165 C) with the rack in the middle position. Line two baking sheets with parchment paper.

Cream: In a large bowl, use a hand mixer or stand mixer on medium speed to beat together butter and sugar until the mixture is pale and fluffy, about 3-5 minutes.

Add wet ingredients: Mix in egg YOLK, oil, and almond extract until just combined.

Add dry ingredients: Sift in baking powder, baking soda, salt, and cornstarch. Mix thoroughly to combine.

Fold in flours: Add in almond flour and all-purpose flour. Gently mix on low or fold with a spatula just until the dough comes together smoothly, with no dry patches.

Shape cookies: Beat egg WHITE with a small pinch of salt for 30s to create an egg wash. Scoop roughly 3-Tbsp portions of dough, rolling into smooth balls. Brush lightly with egg wash. Press egg wash side of each ball firmly into a bowl of sliced almonds, flattening to around ½-inch thickness. Place almond-side up on the lined baking sheets, spacing them about 2 inches apart, 6 cookies per tray.

Bake: 22-25 minutes, or until the cookies have spread, puffed up slightly, and are lightly golden. The edges should be firmly set, with the centers still slightly soft but not raw. These cookies should be crisp, so avoid underbaking!

Cool: Let cookies rest on the tray for 10 minutes to firm up before transferring to a wire rack to cool completely.

Store: Keep in an airtight container for up to a week. Enjoy!