Preheat oven to 400℉. Add sourdough starter, egg, vanilla, salt and sugar to mixing bowl and beat on low until combined.
Add in mix-ins (unless otherwise noted below).
Melt coconut oil on stove and add to bowl, mixing on low until combined.
Add baking soda and mix on low until batter begins to bubble up and grow in size (this is the magic of sourdough starter and baking soda!).
Gently stir in remaining mix-ins.
Line muffin pan with silicone baking cups and add approximately 1/4 cup batter to each muffin cup, filling about 3/4 full.
Bake for 15 minutes, or until a toothpick poked into the center comes out clean.