Sift together 1 3/4 cups powdered sugar and almond flour twice into a large bowl, discarding any large almond pieces that don't pass through. Set aside.

In a stand mixer fitted with the whisk attachment, beat egg whites, cream of tartar, and 1/4 teaspoon salt on medium speed until foamy, about 1 minute. Gradually add granulated sugar and increase speed to high, beating until stiff, glossy peaks form, about 3-4 minutes. Add gel coloring and beat for 10 seconds until evenly distributed.

Add half the almond flour mixture to the meringue and fold gently with a silicone spatula using a J-motion. Add remaining flour mixture and continue folding until batter flows like lava and a ribbon disappears back into itself within 30 seconds — this is the macaronage stage and takes about 40-50 folds total.

Transfer batter to a piping bag fitted with a 1/2-inch round tip. Pipe 1.5-inch circles onto parchment-lined baking sheets, spacing them 2 inches apart. Tap sheets firmly on the counter 5-6 times to release air bubbles.

Let piped shells rest at room temperature for 30-45 minutes until a skin forms and they're dry to the touch. Meanwhile, preheat oven to 300°F (150°C).

Bake one sheet at a time on the middle rack for 14-16 minutes, rotating once halfway through. Shells are done when feet have formed and tops don't wiggle when gently touched. Let cool completely on the baking sheet before removing.

For the buttercream, beat softened butter in a stand mixer on medium-high speed for 2 minutes until pale and fluffy. Gradually add 1 1/2 cups powdered sugar, then add raspberry puree, vanilla, and a pinch of salt. Beat for 3-4 minutes until light and smooth.

Match macaron shells by size and flip half of them over. Pipe or spread 1-2 teaspoons of raspberry buttercream onto the flat side of each flipped shell, then sandwich with the matching top shell. Press gently until filling reaches the edges.

Refrigerate assembled macarons in an airtight container for at least 24 hours before serving to allow flavors to meld and texture to soften. Bring to room temperature 20 minutes before enjoying.