Step 1In a microwave-safe bowl, heat the white chocolate in 15 second increments, stirring in between, until melted and just warm. Stir until smooth. (The white chocolate can also be melted in a bowl set over a pot of simmering water, stirring until melted and smooth; remove from heat before continuing.)
Step 2Slowly whisk in the heavy cream until combined. Whisk in the peppermint extract. Refrigerate the filling until cool and thick but not hard to the touch. It needs to have a spreadable consistency. This makes a scant 1½ cups ganache.
Step 1Heat the oven to 300 degrees and line two cookie sheets with silicone baking mats or parchment. For more accurate rounds, use a permanent marker to draw circles on the underside of the parchment to use as guides (the circles will show through the paper) or place a sheet of marked parchment underneath the silicone mat (the circles should show through if using a dark permanent marker).
Step 2In a medium bowl, sift the powdered sugar over the almond meal and stir to combine. Set aside.
Step 3In the bowl of a stand mixer fitted with the whisk attachment, whip the egg whites and salt on medium-low speed until foamy, about 2 minutes. Increase the speed to medium-high and slowly add the granulated sugar. Continue whipping the egg whites until they form stiff peaks, 3 to 4 more minutes. Add the vanilla and food coloring, if using, beating just until incorporated.
Step 4Remove the bowl from the mixer and carefully fold in one-third of the almond meal mixture until combined, then gently fold in another third. Fold in the last of the almond meal mixture until fully incorporated. The batter should have the consistency of lava, thick but pourable.
Step 5Scoop the batter into a piping bag fitted with a one-half-inch round tip. Squeeze the batter in small rounds, approximately 1½ inches in diameter, onto the prepared cookie sheets. Make sure to leave a couple of inches between the rounds, as they will spread a bit. Once all the rounds are piped, pick up the cookie sheets and smack them on the countertop several times to get all the air bubbles out of the batter. Set the pans aside at room temperature until the surface of each macaron forms a "skin" (it will lose its glossy sheen and will not be sticky when gently touched), 30 minutes to an hour or so (timing will vary depending on the weather, as well as the temperature and humidity inside the kitchen).
Step 6Place the sheet pans in the oven and bake for 9 minutes. Then rotate the pans in the oven (moving the lower pan to the top and vice versa) and bake an additional 9 minutes. If you touch the top of the cookies, they shouldn't sway or wiggle. Cool the cookies a few minutes on the cookie sheet, and then remove the cookies to a wire rack until completely cooled. If the macarons stick to the baking mat or sheet, wait until they are cooled entirely before peeling off the mat to give them time to firm up.
Step 7Fill a pastry bag fitted with a round tip with the cooled ganache. Pipe the ganache onto the flat underside of each of half of the cookies, and form a sandwich using a second cookie of equal size and shape. Roll the edges of the ganache in peppermint crumbles.