Mix the softened butter, brown sugar, flour, nutmeg, and salt until you have soft little crumbs. Set aside and try not to eat it.

In a large bowl whisk together the melted butter, brown sugar, egg, eggnog, and vanilla until smooth and creamy.

Add the sourdough starter and stir it in.

Sprinkle the flour, baking soda, baking powder, salt, and all the warm spices over the top. Fold gently until everything comes together. Do not overmix.

Choose your baking method:

Bake right away if you want muffins on the table fast. They will be soft, fluffy, and perfect.

Cover and let the batter rest for 2-4 hours or refrigerate overnight. This gives the sourdough a chance to do a little work and can make the muffins gentler on digestion and extra tender. It does not make them sour at all.

Scoop the muffin batter into a lined or greased 12 cup muffin tin, or a large 6 cup muffin tin. Fill each cup about ¾ full.

Add a generous spoonful of streusel on top of each one.

Bake at 375 F for 16 to 19 minutes until the tops are golden and a toothpick comes out clean.

Let them cool for a few minutes.

Whisk the powdered sugar, eggnog, nutmeg, cinnamon, cardamom, and vanilla until smooth.

Add more eggnog for a thinner drizzle or more powdered sugar for a thicker glaze.

Drizzle over warm or cooled muffins.