Pierce around the potatoes with a fork and put them on a sheet tray. Drizzle with 2 tablespoons olive oil and season, to taste, with salt and black pepper. Slide them onto the center rack in the oven and bake for 1 hour, then let them cool slightly.
Using a paring knife, slice the potatoes lengthwise and scoop the flesh into a large mixing bowl. Make sure to leave a 1/2-inch thick wall of flesh along the inside of the skin.
In a heavy-bottomed skillet, melt the butter with the remaining tablespoon of olive oil over medium heat. Once warm, saute the garlic and red pepper flakes until fragrant, about 1 minute. Add the Swiss chard leaves and continue sauteing until they are soft and tender and all liquid has been evaporated. Adjust the seasonings with salt and pepper, then transfer the vegetables to a bowl.
Stir the ricotta cheese, mozzarella and Parmesan into the potatoes and season with salt and pepper, to taste. Mash until the filling is creamy, then fold in the Swiss chard.
Using a small spoon, scoop the filling back into the potatoes and pat down the mound so it is secure. Sprinkle more mozzarella and Parmesan over the tops of the potatoes and set them onto a baking sheet. Bake them once more to heat through and to melt the cheese, about 15 to 20 minutes. Remove from the oven and arrange on a serving platter. Serve with softened butter, if desired.