• Preheat the oven to 350℉
• Line a muffin tin with 12 cupcake liners.
• In a large, microwave-safe mixing bowl, melt the butter in the microwave for 20 seconds. Continue to microwave at 15 second intervals until butter is fully melted, stirring between intervals. 
• Add the oil, pumpkin, vanilla, granulated sugar and brown sugar. Mix until smooth. Then add the sourdough starter and continue to mix until smooth.
• Slowly, add the dry ingredients and continue to stir until until mostly smooth with only a few small lumps. If using, add the chocolate chips or nuts and stir until just incorporated.
• Spoon the batter into each cupcake liner until just over ¾ of the way full.

  (You should be able to to divide the batter among all 12 cupcake liners unless you added nuts or chocolate chips. This will increase the volume of the batter and you will have to do a second batch).
• Bake for 30-35 minutes, or until a toothpick inserted into the center of one of the muffins comes out clean.
• Allow to cool completely on a wire rack before adding the maple glaze.

For the Maple Glaze

• Melt the butter in a small, microwave-safe bowl for 15 seconds. If butter is not completely melted, stir, and return to microwave for 10 seconds. Continue to stir and microwave at 10-second intervals until the butter is completely melted.
• Add the milk and maple syrup and whisk together until smooth.
• Add the powdered sugar and continue to whisk until the batter is smooth and thick.
• Use a small spoon to evenly divide the glaze over each muffin.