• If you plan on baking off the muffins right away, preheat the oven to 425°F / 220°C and alternate lining a muffin pan with 6 parchment liners. If you plan on letting the batter rest, proceed with this step after letting the batter rest.
• In a small saucepan set over medium heat, brown the 70g (5 tbsp.) butter for the muffins. Stir the butter occasionally until it turns amber in color and develops little brown specks.
• Take the butter off the heat and transfer to a medium sized bowl. You should be left with at least 55g of butter, no more than 60g. If you have a little less than 55g, add in enough water to reach 55g. Set the butter aside.

Streusel (optional)

• In a small microwave safe bowl, melt the butter. Add in the brown sugar, flour, and cinnamon.
• Stir the mixture together until you have little clumps of dough. Set aside.

Brown Butter Blueberry Muffins

• In a small bowl, whisk together the flour, baking powder, and salt.
• Add the blueberries to another small bowl, and toss them with 1 tbsp. of the flour mixture.
• Whisk the sugar into the brown butter, followed by the egg, vanilla and kefir.
• Add in the flour mixture and fold until only a few flour streaks remain. Then add in the blueberries and fold just until no flour streaks remain.
• (OPTIONAL) Cover the bowl with plastic wrap and let the batter rest at room temperature for at least 30 minutes and up to 1 hour before baking. This will encourage a more flavorful, higher-rising muffin!
• Evenly distribute the muffin batter between the six parchment liners, then top the muffins with the streusel if using.
• Bake the muffins at 425°F for 5 minutes. Without opening the oven door, reduce the temperature to 350°F / 175°C. Bake for an additional 10 minutes, or until a toothpick inserted into the center of the muffins comes out clean.
• Serve and enjoy!