Wow. I mean, wow.
It's a particularly sweet frosting, and the grittiness of the brown sugar comes through on your tongue. Flour - uncooked flour, which I've never seen in a frosting recipe - tempers the sweetness, and the flour/butter/brown sugar combo is really reminiscent of first-stage chocolate chip cookie dough (obviously, no accident!). It's a really nice change from vanilla frosting, and the ecru color is warm and appealing.
I've only used this frosting with chocolate cupcakes, but I could see it complementing something spicy/fruity - apple-cinnamon? pumpkin? - something fall-flavored.
Brown Sugar Frosting (modified slightly)
Makes enough to frost about 24 cupcakes
3 sticks unsalted butter
3/4 cup (5 1/4 ounces) light brown sugar
3 1/2 cups (14 ounces) powdered sugar
1 cup (4 1/4 ounces) flour
3/4 teaspoon salt
3 tablespoons milk
1 tablespoon vanilla
Beat together butter and brown sugar until light and creamy. Add powdered sugar and beat until smooth. Beat in flour and salt. On low speed, mix in the milk and vanilla, then increase speed to medium and beat until smooth and well-blended.