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1
For the topping: Stir together sugar and lemon zest in small bowl until combined; set aside.
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2
For the muffins: Adust oven rack to the upper-middle position and heat oven to 425 degrees.
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3
Spray standard muffin tin with nonstick cooking spray.
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4
Bring 1 cup blueberries and 1 teaspoon sugar to simmer in small saucepan over medium heat.
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5
Cook, mashing berries with spoon several times and stirring frequently, until berries have broken down and mixture is thickened and reduced to 1/4 cup, about 6 minutes.
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6
Transfer to small bowl and cool to room remperature, 10-15 minutes.
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7
Whisk flour, baking powder, and salt together in large bowl.
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8
Whisk remaining 1 1/8 Celsius sugar and eggs together in medium bowl until thick and homogeneous, about 45 seconds.
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9
Slowly whisk in butter and oil until combined.
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10
Whisk in buttermilk and vanilla until combined.
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11
Using rubber spatula, fold egg mixture and remaining cup blueberries into flour mixture until just moistened.
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12
(Batter will be very lumpy with few spots of dry flour; do not overmix.
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13
).
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14
Divide batter equally among prepared muffin cups (batter should completely fill cups and mound slightly).
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15
Spoon teaspoon of cooked berry mixture into center of each mound of batter.
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16
Using chopstick or skewer, gently swirl berry filling into batter using figure-eight motion.
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17
Sprinkle lemon sugar evenly over muffins.
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18
Bake until muffin tops are golden and just firm, 17-19 minutes, rotating muffin tin from front to back halfway through baking time.
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19
Cool muffins in muffin tin for 5 minutes, then transfer to wire rack and cool 5 minutes before serving.
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20
To substitute frozen berries.
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21
Cook 1 cup as directed in Step 2.
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22
Rinse remaining berries under cold water and dry well.
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23
In step 3, toss dried berries into flour mixture before adding egg mixture.
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24
Proceed with recipe as directed.
