Preheat the oven to 425°F. Line 18 muffin tins with cupcake liners or spray the tins with nonstick spray.
In a medium bowl, whisk the sugar, brown sugar, oil, eggs, yogurt, and vanilla.
In a separate bowl, whisk the spelt flour, baking powder, baking soda, cinnamon, and salt.
Gently fold the dry ingredients into the wet ingredients.
Fold the blueberries into the batter.
Fill the muffin tins and place in the oven at 425°F for 5 minutes.
After 5 minutes, turn the oven down to 350°F and bake for another 17 to 20 minutes.
Let the muffins cool in the tins for 10 minutes then remove them and let them cool completely on a wire rack.
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Notes
Don’t overmix: Stir the batter just until the flour disappears. Frozen berries work: No need to thaw the berries. Fold frozen blueberries in straight from the freezer to avoid purple streaks.Even scooping: A large cookie scoop or ¼-cup measure gives evenly sized muffins that bake at the same rate.Oven trick for tall tops: Start at 425°F for 5 minutes, then lower to 350°F to finish baking. This quick heat burst helps the muffins rise high with domed tops.Storage: Cool completely before storing. Keep in an airtight container at room temperature for 2–3 days, or freeze for up to 2 months.