Preheat a griddle pan or large skillet over medium-high heat, or an electric griddle to 350°F.

Make the streusel topping: In a medium bowl, combine the sugar, cinnamon, and butter. Rub the mixture between your pointer finger and thumb until the butter forms pea- sized pieces. Set aside.

Make the French toast: In a shallow dish, use a fork or whisk to beat together the eggs, milk, vanilla, and cinnamon.

Melt the butter on the heated griddle or skillet. Dip the bread in the egg mixture, turning to coat both sides evenly. Let some of the excess drain off, then place the bread slices on the hot griddle pan or in the hot skillet. You may need to work in batches, depending on the size of your griddle or pan. Top each slice of bread with about 1 tablespoon cinnamon streusel. Cook until browned on the first side, 2 to 3 minutes. Flip and cook until the second side is golden brown, 2 to 3 minutes.

Transfer the French toast slices to a plate with the streusel side facing up. Sprinkle with an extra pinch of streusel while the French toast is still hot so it can melt. Repeat with the remaining batches, adding more butter to the griddle or pan if needed.

Serve with butter and maple syrup.