Preheat the oven to 425°F. Prepare 2 large baking sheets with parchment paper. Place the potatoes and cauliflower on the baking sheet, drizzle with 2 tbsp of oil and a tsp of salt. Bake for 20-25 minutes, or until the potatoes are cooked through, tossing once or twice during roasting to ensure even cooking. On a second baking sheet, place the broccoli florets and drizzle with 1 tbsp oil. Roast for 10-15 minutes on a rack beneath the potatoes and cauliflower, tossing once during roasting. Remove from oven and let them come to room temperature.