Make the Macaron Shells

1. Prepare the Dry Ingredients: In a food processor, pulse the powdered sugar and almond flour together to create a fine, smooth mixture. Sift it into a large bowl and set aside.
2. Whisk the Egg Whites: In a clean, grease-free bowl, whisk the egg whites with the cream of tartar until they start to form soft peaks. Gradually add the granulated sugar and continue whisking until stiff peaks form.
3. Fold the Mixture: Add the dry mixture (powdered sugar and almond flour) to the whipped egg whites in thirds. Gently fold the ingredients together using a spatula, being careful not to deflate the meringue. You want the batter to flow slowly like lava when you lift the spatula.
4. Color the Batter: If you want to tint your macaron shells, add food coloring to the batter and fold it in gently.
5. Pipe the Shells: Line a baking sheet with parchment paper or a silicone mat. Transfer the macaron batter to a piping bag fitted with a round tip. Pipe small circles (about 1.5 inches in diameter) onto the prepared baking sheet.
6. Let the Shells Rest: Allow the piped macarons to sit at room temperature for 30-60 minutes until they form a skin and are no longer sticky to the touch.
7. Bake the Shells: Preheat the oven to 300°F (150°C). Bake the macarons for 15-18 minutes, rotating the baking sheet halfway through. The shells should be firm and lightly golden around the edges.
8. Cool the Shells: Let the macarons cool completely on the baking sheet before removing them. This helps ensure they don’t stick to the paper.

Make the White Chocolate Ganache

1. Heat the Cream: In a small saucepan, heat the heavy cream over medium heat until it starts to simmer.
2. Melt the White Chocolate: Remove the saucepan from the heat and add the chopped white chocolate. Stir until the chocolate is completely melted and smooth. If you’d like extra smoothness, stir in the butter.
3. Chill the Ganache: Let the ganache cool to room temperature, then place it in the refrigerator to chill for about 30 minutes until it firms up to a pipeable consistency.

Assemble the Macarons

1. Pair the Shells: Once the shells are completely cool, match them into pairs of similar size.
2. Pipe the Ganache: Using a piping bag fitted with a round tip, pipe a generous amount of white chocolate ganache onto the flat side of one shell of each pair.
3. Sandwich the Macarons: Gently press the matching shell onto the ganache to form a sandwich. Be careful not to press too hard, as the shells are delicate.
4. Rest the Macarons: Allow the assembled macarons to rest in the refrigerator for at least an hour to let the flavors meld together and the filling firm up.