Whisk together the dry ingredients: flour, sugar, baking powder, and salt. Set it aside.
In a separate bowl whisk together the melted butter, oil, sourdough discard, buttermilk, egg, and vanilla extract.
Add the wet ingredients to the dry ingredients and the blueberries and mix until just combined. Do not over-mix.
Divide the batter evenly into the muffin tins.
Top with a sprinkle of crystalized sugar.
Bake the muffins at 425ºF for 5 minutes, then reduce the temperature to 350ºF and continue baking until lightly browned (about 20 minutes).
Notes
Dairy-free Option: Swap the butter for melted coconut oil or vegan butter, and use a dairy-free milk alternative (like almond, oat, or soy milk) with a splash of lemon juice instead of buttermilk.
Storage Instructions: Keep cooled muffins in an airtight container at room temperature for 2–3 days. For longer storage, freeze them for up to 2 months and thaw at room temp or warm briefly in the oven.