A Betty Crocker™ blueberry muffin mix is transformed into a bakery-style loaf with a cinnamon swirl, crunchy streusel topping, and a brown butter maple glaze.
In a medium bowl, mix all Streusel ingredients with your hands for a few minutes until combined, chunky, and shaggy looking. (There should be no flour streaks.) Refrigerate while making the loaf.
In a small bowl, mix the Cinnamon Swirl ingredients until a thick paste forms. Set aside.
Heat the oven to 325°F. Generously grease a 9×5-inch loaf pan with cooking spray.
Place the can of blueberries from the muffin mix box in a fine mesh strainer. Set aside to drain while preparing the batter.
In a large bowl, whisk the 1/3 cup melted butter, 2/3 cup milk, eggs, sour cream, vanilla, and lemon zest until smooth.
Add the muffin mix and 1/2 teaspoon cinnamon. Stir gently just until blended and no dry muffin mix streaks remain. Do not overmix.
In a small bowl, toss the drained canned blueberries and the fresh blueberries with 1 tablespoon of flour. Gently fold the blueberries into the batter.
Pour half of the batter into the loaf pan and spread evenly. Spoon the cinnamon swirl mixture evenly over the batter. Add the remaining batter and gently smooth the surface with a spatula.
Sprinkle the streusel topping evenly over the top of the loaf and gently press into the batter.
Bake for 1 hour 10 minutes to 1 hour 15 minutes, or until the top is golden brown and a toothpick inserted in the center comes out almost clean.
Cool in the pan for 15 to 20 minutes, then remove from the pan to a cooling rack. Cool completely, about 2 hours.
In a medium saucepan, over medium heat, heat butter until melted. Once melted, continue cooking, swirling the pan often. The butter will foam, then the foam will start to subside as brown specks form on the bottom. Keep a close eye on the butter—it can go from brown to burnt quickly. When it smells nutty and caramel-like and turns a deep golden color, remove it from the heat immediately. (The process should take a total of about 5 to 7 minutes.)
Let the browned butter stand for 2 to 3 minutes or until slightly cooled. Whisk in the powdered sugar, salt, and maple extract until the mixture is smooth. It will be thick.
Add the milk and whisk until the glaze is smooth, glossy, and pourable. It should drip slowly from the whisk and coat a spoon in a thin, even layer. If the glaze is too runny add more powdered sugar, if it is too thick add more milk.
Immediately drizzle the glaze over the cooled bread. Let stand for about 15 minutes or until the glaze is set.
Cut into slices to serve.
