01 -  In a large microwave-safe mug, whisk together all-purpose flour, light brown sugar, baking powder, ground cinnamon, ground nutmeg, and salt until evenly distributed. 
 02 -  Add pumpkin purée, milk, vegetable oil, and vanilla extract to the mug. Mix until the batter is smooth and fully integrated. 
 03 -  Microwave the mixture on high power for 1 minute 30 seconds to 2 minutes, or until the muffin rises and the center is just set but moist. 
 04 -  Combine softened cream cheese, powdered sugar, and a pinch of cinnamon in a small bowl. Stir until smooth, then spoon over the warm muffin if desired. 
 05 -  Enjoy while warm directly from the mug.