Sift together the almond flour and powdered sugar. If you can't find almond flour you can always make it with almonds and a food processor. Finely grind the almonds and sift through a fine mesh sifter. Discard or snack on any large pieces.
In a large mixing bowl, add the egg whites. Turn on high and beat until the egg whites form a soft peak meringue.
Add in the granulated sugar, salt, and cream of tartar. Mix on high until a stiff peak meringue forms.
Very lightly and carefully fold in a third of the almond flour/powdered sugar into the meringue with a spatula. All together you'll want to have about 65 turns of this mixture. If you don't mix enough the macaron shell will be extremely fluffy and cracked. If you overmix, the macaron shell will be extremely flat and might not form a foot.
Repeat with the rest of the almond flour/powdered sugar mixture.
Preheat oven to 300 degrees.
Fill a piping bag with the macaron shell filling. I just used a coupler on the end of my piping bag. Pipe macaron shells on the baking sheet. Place the crushed Fruity Pebbles on the tops of each of the macarons.
Let the macarons dry until they are no longer tacky to the touch. It will take 20 minutes to 1 hour.
Place in the oven for about 18 minutes until they no longer stick to the parchment paper.
Let the macaron shells cool.
Frosting
In a mixing bowl, add the butter and creamer. I used fat-free coffee creamer, but regular will work fine! Mix until light and fluffy.
Add in the powdered sugar, vanilla, and milk. Mix on low until the powdered sugar is incorporated. Turn the speed to high and mix for an additional 3 minutes.
Stir in the crushed fruity pebbles. I left some of the fruity pebbles whole, some coarse, and some very fine. The different textures were fun.
Fill the macaron shells with the frosting using a piping bag or sandwich bag. Give the top shell a slight twist to press the frosting down a little. Any other way will crack the shell.