1/4 cup all-purpose flour
1/4 cup white whole wheat flour
1 tablespoon granulated sugar
3 tablespoons light or dark brown sugar
1/4 teaspoon ground cinnamon
Pinch of nutmeg
Pinch of salt
3 tablespoons unsalted butter, melted
1 large egg
1/4 cup light or dark brown sugar
3 tablespoons granulated sugar
5 tablespoons unsalted butter, melted and cooled to lukewarm
3/4 cup sour cream
1 cup white whole wheat flour
1/2 cup all-purpose flour
1 1/2 teaspoon baking powder
1/4 teaspoon baking soda
1/4 teaspoon salt
1 cup diced rhubarb, in 1/2-in pieces
Preheat oven to 375 degrees F. Butter 12 muffin cups.
Streusel: In a small dish, stir together flours, sugars, spices, and salt. Cut in butter until crumbly. Set aside.
Muffins: Whisk egg in the bottom of a large bowl with both sugars. Whisk in butter, then sour cream. In a separate bowl, mix together flours, baking powder and baking soda and stir them into the sour cream mixtue, mixing until just combined and still a bit lumpy. Fold in rhubarb and 1/3 of the streusel mixture.
Divide batter among prepared muffin cups. Sprinkle each muffin with remaining streusel, then use a spoon to gently press the crumbs into the batter so that they adhere. Bake for 15 to 20 minutes, until tops are golden and a tester inserted into the center of muffins comes out clean. Rest muffins in pan on cooling rack for two minutes, then remove muffins from tin and cool them completely.