Step 1

Combine melted butter and sugar in a coffee mug. Stir to combine.

Step 2

Add the milk and 2 tablespoons of lemon juice to the mug ingredients, and stir.

Step 3

Add the flour, baking soda, and salt to the wet ingredients, and stir until incorporated. Stir in the lemon zest.

Step 4

Place the mug into the microwave and heat for 75 seconds, until set and no longer wet in the middle. Check the cake at 60 seconds as microwave cooking times vary.

Step 5

Prepare the glaze by whisking together the confectioners sugar and remaining ½ teaspoon of lemon juice. Adjust sugar and lemon juice as needed to reach desired consistency. Drizzle the glaze on top of the mug cake.

Step 6

Serve the cake in the mug or turn out onto a plate.