Preheat the oven to 275°F.
Pass almond flour and powdered sugar together through a sieve two times to remove large pieces. Set aside for later.
Beat egg whites until foam appears, then add cream of tartar and continue beating for 2 more minutes. Add salt and white sugar then whip for additional 7-8 minutes or until stiff peaks form.
Add food coloring to the egg mixture and whip on low speed until evenly distributed.
Gently fold flour and sugar mixture into the egg white mixture (about 65-75 turns), just until the end result looks like molten lava.
Transfer batter to a piping bag.
Pipe out 1 inch rounds on a baking sheet lined with parchment paper.
Tap the pan hard against a flat surface 3-5 times to release air bubbles in the top layer of batter.
Let macarons rest until the tops become tacky, about 20-30 mins.
Place macaron tray into preheated oven and bake for 19 mins.
Remove tray from oven and let cool completely.
Pipe a circle of buttercream around the edges of half the shells, then fill the circle with apple filling.
Top the filled macarons with the other half of the shells.
Pipe an attractive pattern on top of the macarons with the caramel.