Combine brown sugar, 1 tablespoon flour, and pecans in a small bowl. Stir in melted butter; set aside.
Combine 1 cup all-purpose flour, whole-wheat flour, and next 5 ingredients in a large bowl; make a well in center of mixture.
Stir together egg, buttermilk, and oil; add to dry ingredients, stirring just until moistened. Fold in blueberries.
Spoon about 1/3 cup batter into each of 12 lightly greased muffin cups. Sprinkle batter evenly with reserved pecan mixture.
Bake at 375° for 19 to 21 minutes or until lightly browned. Cool in pans on wire rack 5 minutes. Remove from pans, and cool slightly on wire rack. Serve warm.
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