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Preheat oven to 400.
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Combine 1/4 c. flour, 1/4 c. sugar and cinnamon in a medium bowl.
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Cut in the 3 T. of butter with a pastry cutter or 2 knives, until the mixture resembles coarse crumbs.
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Cover and chill for 30 minutes.
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Place 1 c. sugar and 1/3 c. butter in a bowl and beat with a mixer on high speed for 1 minute or until well combined.
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Add eggs, one at a time, beating well after each addition.
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Combine 2 1/2 c. flour, baking powder and salt, stirring with a whisk.
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Add flour mixture and milk alternately to the butter mixture, beginning and ending with the flour mixture.
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Fold in the blueberries and cinnamon mixture (batter will be thick).
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Spoon batter into 18 muffin cups coated with cooking spray.
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Bake for 18 minutes or until muffins spring back when touched lightly in the center. (I use the toothpick test; if it comes out clean, they're done.)
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Cool in pans for 5 minutes on a wire rack.
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Remove muffins from pans; place on a wire rack to continue cooling.