Combine butter, sugar, and lemon zest in a large bowl and beat until pale and fluffy.

Add the egg and mix until well incorporated, then mix in egg yolk, vanilla extract, and almond extract, followed by lemon juice.

Combine flour and baking powder in a medium bowl and whisk to blend evenly, then fold into the butter mixture gently.

Cover the bowl and refrigerate the dough for 1 hour.

Preheat oven to 350°F (175°C) and line two large cookie sheets with parchment paper.

Use a 1-oz cookie scoop to portion balls of dough, rolling each in chopped sliced almonds if desired.

Bake for 9-11 minutes until puffed and cracked on top, and still soft in the middle.