Step 1

Preheat the toaster oven to 350 degrees F (175 degrees C) according to manufacturer's instructions.

Step 2

Place butter in a medium microwave-safe bowl; heat until just softened, about 10 seconds. Whisk in brown sugar, white sugar, vanilla extract, and salt. Stir in egg yolk. Add flour and baking soda; stir until combined. Stir in chocolate chips. Form cookie dough into 2 balls and place on a small baking tray.

Step 3

Bake in the preheated toaster oven until edges are lightly golden, 8 minutes.