In a microwave-safe mug or ramekin, whisk melted butter with sugars until completely combined. Add egg yolk and vanilla, and whisk well. Whisk in flour and salt, and stir just until combined. Sprinkle top with chocolate chips, and press some into the batter.

Microwave on high power for 30-50 seconds. Watch carefully because it will cook fast and then burn.

Allow to cool for 2 minutes, and then enjoy it while it’s still warm.