Line two baking sheets with parchment paper or silicone baking mats and fit a piping bag with a round tip; set aside.
Wipe the inside of your mixing bowl and whisk attachment with a paper towel lightly dampened with vinegar or lemon juice to remove any grease.
In a medium bowl, sift the powdered sugar and almond flour together twice, discarding any large bits left in the sieve.
In the clean mixing bowl, add the egg whites and cream of tartar and beat on medium speed until foamy.
With the mixer running, slowly sprinkle in 1/3 cup granulated sugar and continue beating until the meringue reaches stiff, glossy peaks.
Add gel food coloring, if using, and beat just until the color is evenly combined.
Add one third of the almond flour mixture to the meringue and gently fold with a spatula, turning the bowl and pressing some of the batter against the sides to deflate slightly.
Repeat with the remaining almond flour mixture in two additions, folding until the batter flows off the spatula in a thick ribbon and disappears back into itself within about 10 seconds.
Transfer the macaron batter to the prepared piping bag and pipe even circles, about 1 1/2 inches wide, onto the lined baking sheets, spacing them about 1 inch apart.
Firmly tap each baking sheet several times on the counter to release air bubbles, then use a toothpick to pop any visible bubbles on the surface.
Let the piped shells rest at room temperature until they form a dry, matte skin on top and your fingertip does not pick up batter when touched lightly, about 20 to 40 minutes.
While the shells rest, preheat the oven to 300°F.
Bake one tray at a time for 14 to 16 minutes, rotating the tray halfway through baking, until the shells have risen and formed feet and the tops look set.
Allow the shells to cool completely on the baking sheets, then gently peel them from the parchment or mats and pair similar sizes together.
To make the raspberry buttercream, beat the softened butter with 2 tbsp granulated sugar and a pinch of salt until light and creamy.
Add the raspberry puree or jam, lemon juice, and vanilla bean paste and beat until smooth and fully combined.
If the buttercream seems too soft, beat in 1 to 2 tbsp of powdered sugar, a little at a time, until it holds its shape.
Transfer the buttercream to a clean piping bag fitted with a small round or star tip.
Pipe a small mound of raspberry buttercream onto the flat side of one shell from each pair.
Gently press and twist a second shell on top to create a sandwich, pressing just until the filling spreads to the edges.
Place the filled macarons in a single layer in an airtight container and refrigerate for 12 to 24 hours for the texture and flavor to mature.
Bring the macarons to room temperature for about 15 to 20 minutes before serving.