Source: Fine Cooking Magazine
Since the preparation can be done the night before, all you need to do in the morning is pop the muffin tin into the oven.
For the streusel:
1/2 cup all-purpose flour
1/2 cup old-fashioned rolled oats
2 tablespoons light brown sugar, packed
1/4 teaspoon ground cinnamon
1/4 teaspoon table salt
3 tablespoons unsalted butter, melted
2 tablespoons pure maple syrup
For the muffins:
5 tablespoons unsalted butter
3/4 cup whole or 2% milk
1/2 cup light brown sugar, packed
3 large eggs
2 teaspoons pure vanilla extract
1 teaspoon ground cinnamon
1/4 teaspoon table salt
8 slices day-old bread, preferably challah or brioche, cut into 1-inch cubes
Make the streusel:
Put the flour, oats, sugar, cinnamon, and salt in a medium bowl, and stir until evenly combined. Add the butter and syrup, and stir until moist clumps form and there are no dusty bits at the bottom of the bowl.
Make the muffins:
Generously coat a standard 12-cup muffin tin with 1 tablespoon of the butter.
In a small saucepan or microwave-safe bowl, melt the remaining 4 tablespoons butter, then transfer to a large bowl. Add the milk, sugar, eggs, vanilla, cinnamon, and salt, and whisk until combined. Fold the bread into the egg mixture until evenly moistened. Divide the soaked bread among the wells, then gently press the top of each to flatten slightly. Sprinkle the streusel evenly over the tops of the muffins, and gently press it down with your hands. Cover the pan with plastic wrap, and refrigerate at least 2 hours or overnight.
Position a rack in the center of the oven, and heat the oven to 350 degrees F. Uncover the muffins, and bake until light golden brown and a tester inserted in the center comes out clean, 20 to 25 minutes. Let the muffins cool in the pan for 5 minutes. Run a thin knife around each muffin, then remove from the pan and transfer to a wire rack. Let cool 5 minutes before serving warm.