Sift powdered sugar and almond flour twice through. Make sure there are no clumps. Whisk well and set aside.
Whisk egg whites until foamy. Add sugar about half at a time. Add extract and food coloring - whisk. Add salt and mix until stiff peaks form. You should be able to turn the bowl over and nothing moves!
Transfer to a mixing bowl and fold in the dry mixture a little at a time in an up-and-over figure-8 motion - this is called macaronage. It’s ready when it falls from your spatula in ribbons. Gently place half the batter in the piping bag with a .25" or .5” tip. You don’t want to lose the volume by squeezing more than necessary.
Prepare baking pan using a 1.5” macaron template under baking mat or smooth piece of parchment paper (you can add a drop of batter to the corners to hold it down). Create macarons by piping from the middle - when it hits the edge of the circle, cleanly release. Fill piping bag as needed. Carefully remove the template. Bang the pan a few times to remove any air bubbles. Gently pop any left with a pin. Let sit in a dry place uncovered for 30-90 minutes until a “skin” forms. They will be dry to the touch.
Bake at 300° for about 15-18 minutes. Check for doneness by lightly tapping the “foot”, or bottom edge, with spatula - it should be firm. If not, put back in the oven for one minute at a time, checking again. When they’re done, remove parchment/mat with cookies from the hot pan and let cool flat before gently removing them.
Make the buttercream by mixing the butter in a medium bowl until smooth. Mix in the honey. Add the powdered sugar and mix well. Pour in 2 tbsp milk and mix until smooth - if it’s too dry, add a bit more milk. Stir in the salt and place in a piping bag. Refrigerate for 15 minutes before use.
Pair up the cookies. turn one over and pipe buttercream in the center, leaving the edge clear. Add the other on top to make a sandwich. Repeat for all. For the best flavor, refrigerate overnight so the buttercream flavor sinks into the cookies. Leave at room temperature for 30 minutes before serving.