Preheat the oven to 350 degrees F. Spray a small baking dish (about 5x7-inches) with nonstick spray.
Cut the potatoes into 1/8-inch-thick slices; set aside.
Melt the butter in a skillet over medium-high heat; add the green onions, red bell pepper, garlic and pinch of ground red pepper. Cook, stirring constantly, for 2 minutes. Add the whipping cream, milk, and salt, stirring well.
Add the potato slices to the pan; bring to a boil over medium heat, and cook, stirring gently, for 15 minutes or until the potato slices are tender. Spoon the potatoes and sauce into the prepared dish; sprinkle with the cheeses.
Bake for 45 minutes or until bubbly and golden brown. Let stand 15 minutes before serving.