Cookies:
1 ¾ Cups confectioners’ sugar
1 Cup almond flour
3 large egg whites, at room temperature
¼ teaspoon cream of tartar Pinch of salt
1/4 cup Blueberry Sugar
2 to 3 drops gel food coloring (see below)
½ teaspoon vanilla, almond or mint extract
Filling:
7 Tablespoons unsalted butter, softened
2 egg yolks
¼ Cup granulated sugar
3 ½ Tablespoons milk
1 teaspoon vanilla extract
Preheat the oven to 300F. Line 3 baking sheets with silicone mats. Measure the confectioners’ sugar and almond flour by spooning them into measuring cups and leveling with a knife. Transfer to a bowl; whisk to combine.
Sift the sugar-almond flour mixture, a little at a time, through a fine-mesh sieve into a large bowl, pressing with a rubber spatula to pass through as much as possible. It will take a while, and up to 2 tablespoons of coarse almond flour may be left; just toss it.
Beat the egg whites, cream of tartar and salt with a mixer on medium speed until frothy. Increase the speed to medium high; gradually add the blueberry sugar and beat until stiff and shiny, about 5 more minutes.
Transfer the beaten egg whites to the bowl with the almond flour mixture. Draw a rubber spatula halfway through the mixture and fold until incorporated, giving the bowl a quarter turn with each fold.
Continue folding and turning, scraping down the bowl, until the batter is smooth and falls off the spatula in a thin flat ribbon, 2 to 3 minutes.
Transfer the batter to a pastry bag fitted with a 1/4-inch round tip. Holding the bag vertically and close to the baking sheet, pipe 1 1/4-inch circles (24 per sheet). Firmly tap the baking sheets twice against the counter to release any air bubbles.
Let the cookies sit at room temperature until the tops are no longer sticky to the touch, 15 minutes to 1 hour, depending on the humidity.
Bake the first batch until the cookies are shiny and rise 1/8 inch to form a “foot,” about 20 minutes. Transfer to a rack to cool completely. Peel the cookies off the mats and sandwich with a thin layer of filling.
Cut butter into pieces, and mash with a spatula until the consistency resembles mayonnaise.
In a small bowl, whisk the egg yolks, then add the granulated sugar, and whisk until the mixture lightens to an off-white and you can no longer see the granules of sugar. Add the
milk, and whisk to combine.
Pour the egg mixture into a small saucepan, and heat over low heat, whisking frequently to ensure that the mixture does not curdle or scorch. Cook until the mixture becomes thick and custardy, like pudding.
Pour the egg mixture back into its bowl, and whisk constantly until it returns to room temperature. Whisk in the butter in three batches, add the vanilla, and stir until smooth and all ingredients are fully combined. Pipe or spread onto one macaron half and sandwich between the other.
