French Buttercream

Pour 1 cup water into a heavy nonreactive saucepan. Add 2 cups granulated sugar, 2 Tbsp. corn syrup, and ¼ tsp. cream of tartar. (The last two prevent the sugar from crystallizing.) Bring to a boil over high heat; continue to cook (you can swirl the pan occasionally, but do not stir!) until sugar dissolves and mixture reaches 230°F, a.k.a. “soft ball stage.” (Be patient and keep your eye on it. Don’t go walking away and watching TV or something.)

Meanwhile, combine 1 large egg plus 5 large egg yolks in the bowl of a stand mixer with the whisk attachment and turn mixer to high speed. Yolk mixture will triple in volume, turn pale yellow, and go to “ribbon stage.” (You can’t overwhip!)

When the sugar is ready, move quickly: Turn off the mixer and add ⅛ tsp. xanthan gum, turn back up to medium-low speed.