Combine : In a 12 oz (340 g) microwave-safe mug, add the melted butter, egg, almond flour, sun-dried tomato pesto, baking powder, and salt.
Mix Batter: Whisk vigorously with a fork until the batter is completely smooth and uniform in color.
Microwave: Cook on high power for 75 seconds. The cake will rise and be firm to the touch.
Loosen Cake: Carefully remove the hot mug and tap the bottom firmly on a plate once to help detach the cake from the sides.
Garnish and Serve: Top with an extra teaspoon of pesto if desired and enjoy immediately, either in the mug or turned out onto a plate.