Preheat the oven to 200°F.
Place the English muffin halves in a baking pan just large enough to hold them in a single layer.
Beat the milk, eggs, sugar, vanilla extract and cinnamon in a medium bowl. Pour the mixture over the English muffins, turning to coat. Let stand 20 minutes, turning once.
Heat a large nonstick skillet or griddle over medium heat. Melt half of the butter and add 4 muffin halves. Cook until the bottoms are lightly golden, about 3-4 minutes. Turn the muffin halves over and cook until lightly golden, about 3-4 minutes longer. Transfer the French toast to an ovenproof pan and hold in the preheated oven. Repeat with remaining muffin halves and butter.
Lightly dust French toast with confectioners’ sugar and serve with warm maple syrup.