Preheat oven to 350 degrees F (175 degrees C). Lightly grease a medium casserole dish.
In a pot with enough water to cover, boil the potatoes 10 minutes, or until tender but still firm. Drain, and set aside.
In a pot, place the cauliflower in a steamer basket over boiling water. Steam 5 minutes, until tender but still firm. Set aside.
Melt the butter in a saucepan over medium heat, and whisk in the flour. Gradually stir in the heavy cream until thickened. Remove from heat, and mix in 1/2 cup Swiss cheese until melted. Season with salt and pepper.
Arrange the potatoes and cauliflower in the prepared casserole dish. Pour the cream sauce over the potatoes and cauliflower, and sprinkle with the remaining Swiss cheese.
Bake 20 minutes in the preheated oven, or until bubbly and lightly browned.