Preheat your oven to 350°F (175°C) and line several baking sheets with parchment paper.

In a medium bowl, whisk together flour, baking soda, baking powder, and salt. Set aside.

In a large mixing bowl, cream the softened butter and granulated sugar together until light and fluffy, about 3-4 minutes.

Add in the egg, almond extract, and vanilla extract, mixing well to combine.

Gradually add the dry ingredient mixture to the wet ingredients and mix until just combined.

Using a cookie scoop or your hands, form balls of dough about 1 inch in diameter and place them on the prepared baking sheets, spacing them about 2 inches apart.

Gently flatten each ball slightly and optionally sprinkle additional granulated sugar on top.

Bake for 8-10 minutes until the edges turn golden. Allow cookies to cool on the baking sheet for 5 minutes before transferring them to a wire rack.

While the cookies cool, mix almond butter, powdered sugar, and 1 tablespoon of milk together for the almond buttercream.

Add more milk if needed for a smoother consistency.

Once cooled, spread or pipe almond buttercream on each cookie and garnish with sliced almonds.