Blueberry Muffin Cake with Cinnamon Sugar (6-inch)

A 6-inch blueberry muffin cake sits precisely at the intersection of breakfast and dessert, and it does not apologize for that. Baked in a spring form, cut into wedges, with a cinnamon sugar top that crackles slightly when you press a fork through it. This is the kind of thing that makes staying in on a Saturday morning feel like the right call.