Chocolate Soufflés for Two

Preheat the oven to 375°F. Brush 1 tablespoon of the butter on two 8-ounce ramekins to grease. Coat the ramekins with cocoa powder, tapping out the excess.
In a large microwave-safe bowl, microwave the chocolate and remaining 2 tablespoons of butter in 30-second bursts, stirring between each burst, until the chocolate mixture is melted and smooth. Use a rubber spatula to stir in vanilla and egg yolks, one at a time.
In a clean bowl, use an electric mixer (stand mixer or hand mixer works) to beat the egg whites, sugar, salt, and cream of tartar just until stiff peaks form. Gently fold the egg white mixture into the chocolate. Spoon into the prepared ramekins.
Make Ahead: At this point, Soufflés can be covered in plastic wrap and refrigerated at this point for up to 1 day.
Bake until puffed and set, about 20 minutes (or about 25 minutes if baking directly from the refrigerator).

While the soufflés are baking, purée the raspberries and sugar in the bowl of a food processor, blender, or with an immersion blender, until smooth. Press the mixture through a fine mesh strainer to remove the seeds.
Garnish the chocolate soufflés with powdered sugar and serve immediately with raspberry sauce.