1. Using a mixer with the whisk attachment, beat the egg whites with the cream of tartar or lemon juice until very soft peaks form.
2. Add slowly the sugar and beat until stiff glossy peaks form.
3. Add the gel food coloring and fold gently into the egg whites with a spatula.
4. Sift the almond flour and confectioners' sugar and mix.
5. Fold slowly the egg mixture into the almond flour and continue folding until it thins out and you can make a figure 8 and it sinks into the dough after about 10 seconds. Consistence is very important.
6. Spoon the macaron batter into a piping bag and pipe batter in about 1.5 inch rounds. I draw the circles on the baking paper to have a guide of the size. Let them sit out on the baking tray until the top is not sticky and forms a skin. This can take about 30-60 min depending on the humidity of the room.
7. Preheat the oven to 300 F / 150 C and bake for about 15-17 minutes or until the macaron shell is not wobbly and doesn't move around when touched. Let the shells cool completely on the baking sheet for about 15 min.
8. The shells are now ready to fill and sandwich together.
9. For the filling, I chose to make simple buttercream with lemon flavour. Whisk the butter for few minutes. Add the sugar and lemon juice and mix. With a piping bag, apply the buttercream. Voila!