Place a well-greased 12-inch cast-iron skillet in a 425° oven for 5 minutes.
Combine first 5 ingredients, stirring with a wire whisk until blended.
Remove skillet from oven. Pour batter into hot skillet.
Bake at 425° for 20 to 25 minutes. (This resembles a giant popover and will fall quickly after removing from oven.)
Combine marmalade, 3 tablespoons butter, and lemon juice in a saucepan; bring to a boil. Add peaches, and cook over medium heat, stirring constantly, 2 to 3 minutes. Spoon on top of baked pancake. Sprinkle with blueberries.