Step 1

Preheat the oven to 400F (200°C).

Step 2

In a small bowl, weigh out the called for blueberries. In another small bowl, transfer about 50g of the blueberries and mash with a fork.

Step 3

In a medium mixing bowl, measure out the called for flour. Remove about a tablespoon of this flour and add it to the bowl with whole blueberries, tossing the blueberries to evenly coat with the flour.

Step 4

Add the salt, baking soda, and baking powder to the flour and whisk to combine.

Step 5

In a large mixing bowl, add the melted and slightly cooled butter with the sugar. Stir to dissolve.

Step 6

Add eggs to the butter and sugar, one at a time, mixing after each until incorporated. Add vanilla.

Step 7

Measure out the sour cream into a measuring cup and combine it with the sourdough starter. Stir until smooth. Add this mixture to the butter/sugar and mix to combine.

Step 8

Add the zest of one lemon (optional), the mashed blueberries, and the sourdough starter mixture to the butter/sugar and mix to combine.

Step 9

Add the flour mixture to the butter/sugar, mixing just until no dry bits of flour remain. Fold in the floured blueberries.

Step 10

Line a 12-cup muffin tin with muffin liners, and fill each well to the rim. Sprinkle coarse sugar over each well (optional).

Step 11

Bake at 400°F (200°C) for 10 minutes then reduce the oven to 350°F (175°C) and bake for 25-30 minutes longer until the tops are slightly golden.

Step 12

Remove muffins from the oven and cool for 5 minutes in the pan. Then remove them to a wire rack. Store loosely covered on the counter.