Preheat oven to 350 degrees. Spray 8 (4-ounce) ramekins or large muffin cups with cooking spray.

Place the chocolate chips and butter in a large microwave-safe bowl and microwave for about 3 minutes or until all the butter has liquefied and most of the chocolate is melted, stirring every 30 seconds. Stir until smooth and glossy. Let cool slightly.

Stir in the flour and powdered sugar. Add the eggs, egg yolks, vanilla, and coffee or coffee liqueur, if using, and whisk until smooth. Divide the batter among the prepared ramekins or muffin cups.

Bake for 9 – 12 minutes, or until the edges are firm but the center is still jiggly (almost runny, but not quite).

Remove the cakes from the oven, let cool for 1 minute, then run a knife around the edges of the ramekins or muffin cups to loosen the cakes. To unmold, invert the ramekins onto individual serving plates. If using a muffin pan, invert the pan onto a large flat surface (like a cutting board) and then gently lift the cakes with a thin flexible spatula and plate on individual serving plates. Serve immediately with whipped cream, ice cream, berries, or a dusting of powdered sugar, if desired.