Step 1

Place a rack in middle of oven; preheat to 350°. Lightly coat a standard 12-cup muffin pan with nonstick spray or line with paper liners. Whisk spelt flour, granulated sugar, brown sugar, and cinnamon in a medium bowl. Add butter and toss to coat. Working quickly, smash in butter with your fingers until pieces are about pea-size. Chill streusel until ready to use.

Step 2

Whisk spelt flour, baking powder, baking soda, cinnamon, and salt in a medium bowl until there are no lumps. Make a well in the center with your hands. Whisk egg, brown sugar, oil, buttermilk, and lemon zest in a small bowl. Pour into well and whisk to combine. Using a rubber spatula, gently fold in blueberries. Evenly divide batter among 8–10 muffin cups, filling each with about ¼ cup batter. Top each muffin with about 1 Tbsp. streusel; bake, rotating pan halfway through, until golden brown and a tester inserted into the center of a muffin comes out clean, 24–27 minutes. Let muffins cool in pan 20 minutes. Turn out onto a wire rack; let cool completely.Do ahead: Muffins can be baked 2 days ahead. Store airtight at room temperature.