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1
Position a rack in the center of the oven; preheat to 400.
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2
Brush the insides of 10 muffins cups with softened butter, then brush the top of the pan.
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3
Make the streusel: mix the flour, superfine sugar, brown sugar, cinnamon, butter, and vanilla with your fingers in a small bowl until combined and crumbly; set aside.
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4
Grate the zest from the orange; set aside.
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5
Juice the orange and measure; you should have 1/3 cup.
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6
Whisk the oil, milk, orange juice, orange zest, and eggs together in a bowl.
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7
Whisk the flour, brown sugar, baking powder, and salt together in another bowl.
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8
Add to the liquids and stir with a spoon just until combined; do not overmix.
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9
Fold in blueberries.
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10
Using a 2 1/2 inch diameter ice-cream scoop, portion the batter, rounded side up, into the prepared muffin cups.
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11
Generously sprinkle with the streusel.
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12
Bake for 10 minutes; decrease oven temperature to 375 and continue baking until the tops of the muffins are golden brown and a cake tester comes out clean, about 15 minutes more.
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13
If using frozen berries, allow a few extra minutes.
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14
Cool in pan on wire rack for 10 minutes; remove muffins from pan to wire rack and cool completely.
