1In a shallow dish or pie plate, whisk together the eggs, sugar, vanilla, salt and milk. Place the bread slices in the custard base, flipping once or twice to saturate them well, and let stand for about an hour (or overnight), until the bread is even more saturated.
2Preheat the oven to 350?F. Set a heavy skillet over medium heat. Melt the butter, swirling to coat the bottom of the pan. Lift each bread slice from the custard base and place in the pan. Cook the slices for about 3 minutes, occasionally pressing them against the bottom of the pan with a spatula so the bottoms cook evenly. This step seals the bottoms of the slices by creating a crusty bottom, preparing the bread to absorb more custard base.
3Spoon or ladle more of the egg mixture into the centre of each bread slice, if it will take more without running down the sides or out the bottom. Cook for another minute, pressing the slices slightly to seal. When the slices are full of custard, carefully transfer the skillet to the middle rack of the oven without flipping.
4Bake for 15 minutes, and then gently shake the pan. If the custard base is still liquid, continue baking and check again. It should take about 20 minutes (depending on the thickness of the bread) to cook all the way through. The French toast is done when the custard seems solid and each slice appears puffed, as the custard souffles when fully cooked.
5Using the spatula, remove the French toast from the skillet and place them, caramelized-side up, onto the plates. Serves 2-4 (they're pretty thick).