These muffins are best served right out of the oven and spread with room-temperature butter. You can substitute the crème fraîche called for in the recipe with sour cream or plain yogurt; buttermilk might work just as well. To prevent the mixture from turning blue, you may want to toss the berries in a tablespoon of flour, or you can fold in the berries when there is a little bit of flour left in from the dough. Both ways work equally well.
1 1/2 teaspoon (7 grams or 1/4 ounce) baking powder
1/4 teaspoon (1 gram) baking soda
1/4 teaspoon (2 grams) fine grain sea salt
3/4 cup (3 3/4 ounces or 105 grams) blueberries, fresh or frozen (if frozen, don't bother defrosting)
Preheat oven to 375 degrees. Line a muffin tin with 12 paper liners, or butter each cup. Using the paddle attachment on your electric mixer, beat the butter and sugar with until light and fluffy. Add in the egg, and beat well. Next, add in the crème fraîche and lemon zest. Put flours, baking powder, baking soda and salt into a sifter and sift half of the dry ingredients over batter. Mix just until combined. Sift the remaining dry ingredients into batter and mix just until the flour disappears (don't overmix). Gently fold in the blueberries. The mixture will be quite thick (and even thicker, if you used a full-fat Greek-style yogurt), similar to a cookie dough, which is why an ice cream scoop (I used a 1½-ounce scoop) is a great tool to fill your muffin cups. You're looking for them to be about 3/4 full, nothing more, so you might only need less than 12 cups. Bake for 23 to 30 minutes, until the tops are golden and a tester inserted into the center of muffins comes out clean. Let cool on a wire rack (if you're into that stuff) or once out of the oven, break open with a fork, and serve with a generous pat of butter. Enjoy!