• Preheat the oven to 425℉ and line your muffin tins with 12 liners.

For the streusel

• In a small bowl, make the streusel. Combine flour, cinnamon, nutmeg, white sugar, and cold cut up butter. Using your hands, mix it together until combined into a crumbly, streusel mixture. Set aside while you make the muffin batter.
  3/4 cup all-purpose flour, 5 tbsp unsalted butter, 1/3 cup white sugar, 1/2 tsp cinnamon, 1/4 tsp nutmeg

For the muffins

• In a medium-sized bowl, add flour, salt, cinnamon, nutmeg, cornstarch, baking powder, and baking soda. Using a spatula, mix until just completely combined and set aside.
  2 1/2 cups all-purpose flour, 1 tsp baking soda, 2 1/2 tsps baking powder, 1 tsp cinnamon, 1/2 tsp nutmeg, 1 tbsp cornstarch, 1/2 tsp salt
• Into a large bowl, add oil and white sugar and whisk together. Then add in the eggs and vanilla and continue whisking. Then add in the eggnog, rum extract (optional), and sour cream. Whisk until everything is well combined and smooth.
  1/2 cup oil, 3/4 cup white sugar, 3 eggs, 3/4 cups eggnog, 1/4 cup full-fat sour cream, 1 tbsp vanilla, 1/4 tsp rum extract
• Pour the dry ingredients into the wet and using a spatula, gently fold to create a soft muffin batter.
• Evenly divide the batter between 12 liners, they should be almost or all the way full. Using a cookie scooper helps big time to minimize the mess. Sprinkle streusel on top.
• Bake the muffins at 425°F for 5 minutes, then lower the temperature to 350°F (do not open the oven door) and bake for an additional 12-15 minutes. The muffins are ready when they bounce back at touch or a toothpick inserted comes out clean.
• These muffins stay fresh covered at room temperature for a few days, or in the refrigerator in an airtight container for up to 1 week!