Chocolate Soufflés with Blood Orange Sauce

Combine all of the ingredients in a 1-quart saucepan. Bring to a simmer over medium-low heat and cook, stirring occasionally, until the sauce is reduced to 1-1/2 cups, about 45 minutes. Strain through a fine sieve into a small bowl, pressing on the solids to extract all the liquid; discard the solids. Refrigerate, stirring occasionally, until cold. The sauce will thicken as it cools. Serve cold or gently reheat and serve warm.

Position a rack in the lower third of the oven and heat the oven to 375°F. Generously butter eight 6-oz. ramekins (3-1/2 inches in diameter and about 2 inches deep). Coat the insides with sugar, tapping out any excess.

In a 3-quart saucepan, whisk together the egg yolks, milk, sugar, cornstarch, cocoa powder, and salt. Over medium heat, whisk until the mixture bubbles, about 4 minutes; it's OK if it's lumpy at this point. Continue simmering while whisking until smooth and very thick, about 2 minutes more. Remove from the heat and whisk in the chocolate, butter, and vanilla until smooth and glossy. Transfer to a large bowl set in a larger bowl of ice water and whisk often until cooled to room temperature, about 10 minutes.

In a stand mixer fitted with the whisk attachment (or in a large bowl, using a hand-held electric mixer), beat the egg whites on high speed until foamy, about 30 seconds. With the motor running, add the cream of tartar and continue beating until the bubbles become smaller and the whites almost form soft peaks, 30 to 60 seconds more. With the motor still running, add the confectioners’ sugar 1 Tbs. at a time and beat until the whites hold a glossy, pointed, stiff peak when you remove the beater, about 30 seconds more. If the peak droops, finish whisking them to stiff peaks by hand to avoid overbeating.

Stir the pastry cream with a large silicone spatula to loosen it, then stir in a third of the meringue until combined. Gently fold in another third of the meringue by starting at the edge of the bowl and slowly bringing the spatula up through the middle of the pastry cream and then back to the edge of the bowl, rotating the bowl and repeating this motion until the meringue is mostly incorporated. It's OK if there are a few white streaks at this point. Add the remaining meringue and fold until just combined, leaving no white streaks visible.

Divide the soufflé mixture evenly among the prepared ramekins and smooth the tops with an offset spatula. Run your index finger around the edges of the ramekins to create a shallow trench. Put the ramekins on a large rimmed baking sheet and bake until a skewer inserted in the center of a soufflé comes out with just the tip still wet, 15 to 20 minutes. Dust the soufflés with confectioners’ sugar, if you like, and serve immediately with the sauce of your choice, if using.