Preheat the oven to 400°. In an 8-9 inch cast iron skillet, arrange the apples snugly, cored side up. Add the maple syrup, honey and 2 tablespoons of the butter and bring to a simmer over high heat. Reduce the heat to low, cover and cook, gently shaking the pan occasionally, until the apples are tender, 5 minutes.
Uncover and cook over high heat, shaking the pan a few times, until the liquid is evaporated and the apples are caramelized, about 7 minutes.
Arrange the bread slices in a square on a work surface. Trim the corners of the slices to form a round the size of the skillet. Spread the bread with the remaining butter.
Arrange the bread over the apples, buttered side up, and sprinkle with sugar. Bake for 20 minutes, until the bread is toasted. Invert the Charlotte onto a plate.
Cut into wedges and serve warm with a dollop of sour cream.