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Preheat oven to 400 degrees and line a muffin tin with liners.
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In a bowl, mix flour, granulated sugar, brown sugar, baking powder, baking soda, and salt together.
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Make a well in the center of the dry ingredients and pour in the buttermilk, vegetable oil, and two eggs. Mix until batter is just combined (it will be thick).
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Add in lemon zest, lemon juice, sour cream and vanilla extract. Mix until just combined.
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Toss blueberries in 1 Tbsp of flour (this prevents the blueberries from sinking to the bottom of the batter) and add to the batter. Mix.
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Fill muffin cups about 2/3 of the way full with the lemon blueberry muffin batter (batter will make about 18 muffins or so). Set aside.
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In a separate bowl, mix lemon zest, flour, and brown sugar together. Pour in melted butter and mix together until crumbs form.
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Generously sprinkle crumbs into each muffin tin, pressing the crumbs down lightly into the batter.
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Bake for 16-18 minutes, or until muffins are just golden brown and a toothpick comes out clean.
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Mix powdered sugar and lemon juice. Drizzle the glaze over the muffins (it’s best to allow the muffins to cool about 5-10 minutes before adding the glaze).
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Enjoy!