Separate eggs and allow egg whites to come to room temperature.
Sift almond flour and powdered sugar together into a bowl.
In a clean bowl, beat egg whites with cream of tartar until foamy, then gradually add granulated sugar and beat until stiff peaks form.
Gently fold dry ingredients into the meringue in batches, being careful not to overmix; batter should flow like lava.
Divide batter into portions and color with gel food coloring.
Transfer to piping bags and pipe oval shapes onto parchment-lined baking sheets.
Tap sheets firmly to release air bubbles, then let rest for 30–60 minutes until tops are dry to the touch.
Bake at 300°F (150°C) for 14–16 minutes. Let cool completely.
To make the buttercream, beat butter until creamy. Add powdered sugar, vanilla, salt, and cream; beat until fluffy.
Pipe buttercream onto one macaron shell and sandwich with another.
Decorate with food-safe markers or sprinkles if desired.