Skip buttery, sugary streusel and try topping your coffee cake with crunchy honey-sweetened muesli instead. It's better for you and just as delicious.
Preheat oven to 350 degrees. Butter a 9 1/2-inch tube pan; dust with flour. Whisk together flour, baking powder, baking soda, and salt in a bowl. In another bowl, beat butter on medium speed until smooth, about 1 minute. Gradually beat in sugar until mixture is pale and fluffy, about 2 minutes. Add eggs one at a time, beating to combine after each, then beat in vanilla. Add flour mixture in 3 batches, alternating with 2 additions of buttermilk, beating until just combined (do not overmix).
Combine muesli and honey in a small bowl. Spread half of batter in prepared pan. Top evenly with blueberries. Spread remaining batter on top, then crumble muesli mixture over batter, pressing gently to adhere. Bake until a tester inserted in middle comes out clean, about 1 hour, 10 minutes (if cake is browning too quickly, tent with foil). Cool completely, at least 1 1/2 hours, before removing from pan. Cake can be stored at room temperature up to 2 days.
The cake can also be topped with a simple glaze: Whisk together 1 cup confectioners' sugar and 2 tablespoons milk until smooth, then drizzle the mixture over the cooled cake; let set 20 minutes before serving.