Line a cookie sheet with a silicone mat or you can use parchment paper if you don't have one.
Add the powdered sugar and almond flour to a food processor and pulse until fully combined and rid of lumps. Sift the dry ingredients into a large bowl. If you don’t have a food processor you can just sift the ingredients together.
In a medium bowl, prepare the french meringue. Beat the egg whites on low speed with a hand mixer until they get frothy. Increase the speed and slowly add the sugar. Beat until stiff peaks form.
Split the meringue in half and into separate bowls. Add one drop of red food coloring to one bowl and one drop of blue food coloring to the other. Mix until the color is fully combined in each meringue.
Split the dry ingredients in half and add each half to the meringues and begin to gently fold with a silicone spatula. This process is called macaronage. You will know the batter is ready when the ingredients are fully combined and not streaky. You should be able to hold the spatula above the bowl and draw a figure 8 smoothly without the batter breaking off. Transfer the batter to a piping bag fitted with a piping tip. Pipe 1-inch disks onto the prepared cookie sheet.
Firmly tap the cookie sheet onto the counter 3 or 4 times to bring any air bubbles to the surface. Use a toothpick to pop any remaining air bubbles.
Allow the macarons to rest for an hour or until the tops of the macarons have dried. You will be able to gently run your finger over them without anyting getting on your finger.
Preheat the oven to 280 degrees (F).
Place the macarons on the middle rack of the oven and bake for 5 minutes, rotate the cookie sheet and bake for another 5 minutes, rotate the pan one last time and bake for 5 minutes. 15 minutes in total.
Remove from the oven and allow to cool completely on the cookie sheet.
If the macarons were baked correctly they should easily peel off of the silicone mat.
For Vanilla American Buttercream:
In the bowl of a stand mixer or in a medium bowl with a hand mixer, beat the butter until very soft and fluffy.
Add the vanilla and half of the powdered sugar. Beat until fully combined.
Add the rest of the powdered sugar and the heavy cream and beat for 5-6 minutes or until the buttercream is light and fluffy.
If the buttercream is too thick you can add more heavy cream.
Transfer the buttercream to a piping bag and pipe the desired amount of buttercream onto the inside of a macaron shell. Sandwich another macaron shell on top.