If your pan isn't big enough to cook all the French toast at the same time, heat the oven to 200°F. In a large bowl, whisk together the eggs, cream, half-and-half, cinnamon, sugar, nutmeg, and vanilla.
Place the cornflakes in another large bowl and crush with your hands until the pieces are small (but not like breadcrumbs) and somewhat uniform in size. Place a rimmed baking sheet nearby to hold the prepared bread.
Dip a slice of bread into the cream mixture, immersing both sides (saturate it, but do not let it fall apart).
Dip the slice into the cornflakes on both sides, pressing to adhere the flakes; set aside on the baking sheet. Repeat with the remaining slices.
Place a griddle or wide (preferably 14-inch) sauté pan over medium heat for several minutes. If using an electric griddle, set the heat to 350°F.
Sprinkle the griddle with a few drops of water; they should bounce around before evaporating. If they sizzle away quickly, the heat is too high. If they just sit there and slowly steam, the heat is too low. When the griddle is properly heated, add 1 Tbs. clarified butter for each piece of French toast and tilt to coat the pan.
Add the prepared bread in an even layer. Cook until golden on one side, about 4 minutes. Lift each piece with a spatula and put 1/2 Tbs. butter in its spot. Flip the toast onto the butter to cook the other side, about 4 minutes more. Repeat with the remaining slices of bread. Serve immediately or keep warm in the oven until all the French toast is cooked.
Cut each piece of bread in half diagonally to make triangles. Arrange 3 triangles like shingles on serving plates, sprinkle with confectioners' sugar, if desired, and serve with softened butter and maple syrup.