Chocolate chip cookie in a mug

Put the butter in an 8 oz mug and microwave 20 to 30 seconds, until almost all melted but not boiling hot.

Add the light brown sugar to the partially melted butter.

Add the granulated sugar, a pinch of salt and a drop of vanilla.

Stir with a fork to a paste. Add the egg yolk and stir in.

Sprinkle in the flour and stir just until combined; a few streaks are fine.

Add the chocolate chips (and any add-ins such as sprinkles, chopped nuts or toffee) and mix until no flour streaks remain. Sprinkle a few chips on top.

Microwave on high 45 seconds to a minute, until puffed and the centre looks dry; if not dry, add 10-second increments.

Serve as is or with ice cream on top; let cool a minute or two first, it is very hot.