Preheat the oven to 400F.
Grease the inside of 4 8-ounce small ramekins with butter, dust with cocoa powder, and tap out any extra.
Place the 1/2 cup chocolate chips and butter in a medium microwave-safe bowl and microwave in 30 second increments, stirring, until melted and smooth.
Stir the sugar and flour into the chocolate mixture.
Add in the eggs and mix until smooth.
Pour the half batter into the four cups, place a few pieces of chocolate chips or chopped chocolate (this creates an extra chocolate lava explosion!) and then fill ramekins with remaining batter. They should be about 3/4 full. Place the baking ramekins on a baking sheet.
Bake for 14-16 minutes, until the top and edges are set, but center is still jiggly. Let cool slightly for 2-3 minutes in the ramekins.
Using a small knife, gently loosen the edges of the cakes from the ramekins. Invert onto a plate, tapping gently to release the cakes. Serve the cakes warm, with a scoop of vanilla ice cream, a drizzle of chocolate sauce or whipped cream on top, if desired.