Oozing Chocolate Orange Cakes

1/3 cup granulated sugar, plus more for dusting ramekins (divided)
9 ounces bittersweet chocolate, chopped
3/4 cup (1 1/2 sticks) unsalted butter, cut into cubes
3 eggs
3 egg yolks
1 tablespoon all-purpose flour
3 tablespoons grated orange zest (about 3 medium oranges),
    or more to taste
3 tablespoons Grand Marnier liqueur

Heat oven to 425 degrees F. Butter 8 small ramekins and sprinkle with sugar, tapping out any excess. Place on a baking sheet.

Place chocolate and butter in a heavy saucepan. Melt over medium-low heat until smooth.

Meanwhile, place the eggs, egg yolks and 1/3 cup sugar in the bowl of an electric mixer fitted with the paddle attachment. Beat on high until mixture is thick and yellow, 7 to 9 minutes. Gently fold half of the melted butter and chocolate mixture into the egg mixture until fully incorporated. Fold in the remaining chocolate mixture until fully incorporated and no dark streaks remain.

Fold in the flour, orange zest and liqueur, and divide batter among the ramekins. If you want only some of the cakes to have an orange flavor, stir zest and liqueur into batter-filled ramekins individually, using 1 teaspoon grated zest and 1 teaspoon Grand Marnier per ramekin. (Cakes can be prepared to this point up to 1 day ahead. Cover baking sheet with plastic wrap and refrigerate. Let batter come to room temperature before baking.)

Bake until edges are puffy and center is still slightly jiggly, about 11 to 13 minutes.

Raspberry variation: Omit orange zest and Grand Marnier. Fill ramekins half way, then add 3 to 5 fresh raspberries and a teaspoon of Chambord (raspberry-flavored) liqueur per ramekin. Top with remaining batter.

S'more variation: Omit orange zest and Grand Marnier. Fill ramekins half way, then add 1 tablespoon caramel ice cream topping and 10 miniature marshmallows per ramekin. Top with remaining batter.