Preheat your oven to 390°F (200°C). Lightly grease a 6 oz ramekin with butter or oil spray.
In a small bowl, melt the chocolate chips and butter together in the microwave for 30–45 seconds. Stir until smooth.
Add vanilla extract, then whisk in the egg and sugar until well combined.
Gently fold in the flour and salt until just incorporated.
Pour the batter into the prepared ramekin.
Bake for 10–12 minutes until the edges are set and the center remains slightly soft.
Let cool for 1–2 minutes, then carefully invert onto a plate or enjoy straight from the ramekin.
Dust with powdered sugar if desired. Serve warm.