FOR THE CRUMB TOPPING: – 1/2 cup (60g) all-purpose flour – 1/4 cup (50g) firmly packed light brown sugar – 1/4 teaspoon ground cinnamon – pinch of salt – 3 tablespoons (42g) unsalted butter, cold and cut into 1/2-inch cube FOR THE MUFFINS: – 1 & 3/4 cups (210g) all-purpose flour – 1 teaspoon baking powder – 1/2 teaspoon salt – 1/4 cup (57g) unsalted butter, softened – 1/2 cup (100g) firmly packed light brown sugar – 1/2 cup (140g) cookie butter (such as Biscoff or Trader Joe's Speculoos Cookie Butter) – 1 large egg – 1/2 teaspoon vanilla extract – 3/4 cup milk