French Macarons with White Chocolate Ganache

1. 1Combine the powdered sugar and almond meal in the bowl of a food processor fitted with the metal blade. Process until the sugar and almond meal are combined, scraping down the bowl a few times to ensure they’re evenly mixed and being careful not to over-mix (the almond meal will eventually turn pasty, which is you don’t want to happen). Transfer the mixture to the bowl of an electric mixer fitted with the paddle attachment, scraping with a spatula to make sure you’ve transferred everything (losing even a small amount of the sugar-almond mixture can throw off the whole recipe).
2. 2Add 55 grams of the egg whites and beat until well combined. Set aside.
3. 3Place the remaining 55 grams of egg whites in the bowl of a stand mixer fitted with the whisk attachment and set aside. Combine the filtered water and granulated sugar in a very clean saucepan over medium-low heat, using a candy or infrared thermometer to check the temperature of the syrup as it cooks. When the syrup reaches 220°F, start beating the egg whites until they’ve achieved soft peaks. When the syrup reaches 244°F, pour it slowly and carefully into the beaten egg whites by trickling it in a steady stream down the edge of the mixing bowl. Whip until the meringue cools to 104°F.
4. 4Place the bowl containing the reserved sugar-almond mixture back in the stand mixer fitted with the paddle attachment. Add about 1/5th of the meringue to the sugar-almond mixture and beat to combine. Remove the bowl from the stand mixer and, by hand, gently fold in the remaining meringue until it’s evenly combined—make sure you can’t see any white spots in the mixture, which would yield uneven cookies. But don’t overmix, either: You want to avoid deflating the meringue.
5. 5Scrape the macaron mixture into a pastry bag fitted with a small tip; twist the top of the bag closed. Alternately, scrape the mixture into a resealable plastic bag and snip about a 1/3 inch off a bottom corner.
6. 6Line two baking sheets with parchment paper and pipe out 1 1/2–inch circles (these will spread to 2 inches as they bake). Note that for macarons, parchment paper works better as a lining than Silpat mats. Also, thinner baking sheets are better than heavier ones, since the greater heat conducted from the bottom allows for evenly baked cookies. If you’d like to decorate with candy sprinkles, now’s the time to add them, sprinkling over the macaron tops and gently tamping with a finger to make sure they embed in the batter.
7. 7Bake in a convection oven at 295°F, or in a conventional oven at 320°F until done, 15 to 18 minutes. Avoid browning—the base of the cookies should be straight rather than slumped, and you shouldn’t notice any air gaps in the cookies’ texture.
8. 8To check for doneness, lift a corner of the parchment paper and carefully slide a finger underneath the paper and a macaron while gently peeling the paper back. The bottom should be flat and come off easily and the tops shouldn’t give when lightly tapped by a fingertip. Do not check doneness more than once or twice during baking: Opening and closing the oven will mess with their baking time, and you’ll risk making the cookies collapse. When the cookies are done, transfer, on the parchment paper, to cooling racks.
9. 9Once the macarons have cooled completely, you can decorate them with the optional food colors, using pastry brushes to splatter or paint the tops (or both).

To make the ganache:

1. 1Put the chopped white chocolate in a medium heatproof mixing bowl and set aside. Place the cream and scraped vanilla seeds or extract in a small, heavy saucepan and set over low heat until it begins to simmer. Immediately pour the cream over the chocolate and let it sit for 2 to 3 minutes. Whisk, starting from the center and continuing until the chocolate is melted and the mixture is smooth.
2. 2Cover the ganache mixture with plastic wrap, making sure the plastic touches the top surface. This will prevent a skin from forming. Cool in refrigerator for at least 2 hours, or as long as overnight.

To assemble:

1. 1Pair macarons of similar size. Remove the ganache from the refrigerator. If you choose to pipe the ganache, transfer it to a pastry bag fitted with a small tip or a resealable plastic bag with about a 1/2 inch snipped off a bottom corner. Squeeze the ganache to about the size of a cherry (about 1 teaspoon) onto the center of a macaron half. Top with another half and press gently so that it looks like a mini hamburger; the filling should not ooze out the edges. Refrigerate, covered, at least 24 hours before serving.