Preheat oven to 325° F (160° C). Line 3 large cookie sheets with parchment or a silicone mat with 1 ½-inch circles.
Prepare a double boiler with water for a gentle simmer.
In the bowl of a stand mixer, add the 90 g egg whites with the sugar, salt and cream of tartar. Place the bowl over the double boiler and heat to 150F to dissolve the sugar. Stir the mixture constantly while heating.
Return the bowl to your stand mixer fitted with the whisk attachment. Mix on high for 10 minutes, or until stiff peaks form. The bowl will be cool to the touch. Add your vanilla extract now.
While the mixer is running, sift together the almond flour and powdered sugar. Add in the 80 grams of egg whites and mix until a paste forms.
Fold in 1/3 of the whipped meringue. Repeat until all the meringue is mixed in. Press the mixture during the folding to remove any air bubbles. Continue folding and pressing until the batter runs off your spatula in a ribbon.
Fit a large pastry bag over a tall glass. Fold the top of the bag over the edge of the glass. Fill the bag about 2/3 full.
Pipe batter out on the silicone mat, making them smaller than the circles. Firmly bang the cookie sheet on the counter 5 -10 times to release any trapped air bubbles. Pop bubbles with a toothpick and smoother over. Add sprinkles.
Bake the macarons fir 10 - 12 minutes.
Remove from the oven and immediately move the mat with the macarons to a cooling rack to cool completely.
For the buttercream beat the butter for 2 minutes until smooth and creamy. Add in 1/4 of the powdered sugar, heavy cream, mint extract and salt. Gradually continue adding the powdered sugar until just combined. Beat for 5 minutes, adding in any up to another tablespoon heavy cream if the mixture is too thick.
Pip filling on to the "bottom" macaron shell and then top with the decorated one.
Keep refrigerated for up to 5 days, or freeze up to 2 months.