Using an 8oz mug (or larger), microwave the butter or oil for about 15 seconds until just melted. Remove and whisk in the dry ingredients.
Add vanilla, milk and seed butter, stirring till just combined.
Microwave for around 1 minute and 30 seconds, depending on the power level of your microwave. Higher power requires less time. This may take a few tries to really test as microwaves vary greatly, but it's better to go with a lower cook time so the cake doesn't dry out.
Allow the mug to cool (it will be very hot for a few minutes) and top with powered sugar, whipped cream, ice cream, or berries. Serve warm.
Notes
For gluten free, use 2 tablespoons of brown rice flour and 2 tablespoons or oat flour or Bob's 1:1 all purpose flour.
For dairy free, use coconut oil or earth balance pressed oils instead of butter. Use any milk you like.
If you aren't sensitive to nuts, nut butters can be substituted for the seed butters.