Mix flour, sugar, baking powder and salt

Mix milk, melted butter and vanilla essence

Mix dry and wet ingredients until combined

Add in the lemon zest and lemon juice whisk well

Set microwave to 4 minutes, if yours is powerful set to 2 minutes. Put the mug with the cake batter into the microwave. Check at 2 minutes to see if done by tapping the center, it should be firm and not wet

Enjoy immediately