Preheat your oven to 375°F and line a muffin tin with paper liners (or grease it if you prefer).
In a large bowl, whisk together the flour, sugar, baking powder, baking soda, and salt.
In a separate bowl, mix your potato flake sourdough starter, buttermilk, egg, and vanilla extract until smooth.
Slowly add the wet ingredients to the dry, stirring gently until just combined. Be careful not to over mix—you want these muffins light and fluffy! Fold in the blueberries.
Prepare the Streusel:
In a small bowl, mix the flour, brown sugar, and cinnamon. Cut in the cold butter using a fork or your hands until it resembles coarse crumbs.
Spoon the batter into the prepared muffin tin, filling each cup about 2/3 full. Sprinkle the streusel generously on top of each muffin for that irresistible crumbly finish.
Pop the muffins into the oven and bake for 20-25 minutes, or until a toothpick inserted into the center comes out clean. Your kitchen will smell like heaven!
Let the muffins cool in the tin for 5 minutes before transferring them to a wire rack. Now comes the hardest part—waiting for them to cool enough to eat! But trust me, it’s worth the wait.
If you want to bulk ferment these muffins, omit the baking powder and wait 8 or more hours before adding salt, vanilla, blueberries and baking soda. (These ingredients are adding just before baking.)