Sift together the almond flour and 100g powdered sugar in a bowl. Discard any large almond pieces.

In a grease-free mixer bowl, whip egg whites and cream of tartar until frothy. Gradually add granulated sugar and whip until soft peaks form. Add blue gel food coloring and whip until stiff, glossy peaks form.

Gently fold the dry ingredients into the meringue using a spatula (macaronage). Fold until the batter runs off the spatula in smooth, continuous ribbons like lava.

Pipe the batter into 1.5-inch circles on prepared baking sheets. Tap the sheets firmly on the counter to release air bubbles.

Let the macarons rest at room temperature for 30-60 minutes until a dry skin forms on the surface.

Preheat oven to 300°F (150°C). Bake for 14-16 minutes until the shells do not wobble when nudged. Let cool completely.

Make the buttercream: Beat softened butter until fluffy. Gradually add 1.5 cups powdered sugar, vanilla, salt, and heavy cream. Beat until light and creamy.

Assemble: Pipe buttercream onto a bottom shell. Place a top shell on at an angle. Press a mini cookie into the frosting 'mouth'. Attach candy eyes with a tiny dab of buttercream.