Preheat oven to 425 degrees. Fill large pot with potatoes and salted water. Bring to a boil over high heat and cook until potatoes are fork tender, about 15 minutes. When potatoes have finished cooking, drain water and set potatoes aside in bowl or colander. While potatoes are cooking, line rimmed baking sheet with parchment paper. To prepare broccoli, remove bottom part of stem and slice into bite-sized florets, leaving an inch of the stem intact. Place broccoli on prepared baking sheet, lightly drizzle with 1 teaspoon olive oil, and sprinkle with pinch of salt and 1/2 teaspoon garlic. Roast in oven for 20 minutes until crispy. Heat 1 teaspoon olive oil over medium heat. Sauté leeks, crushed red pepper, and garlic until leeks soften, about 1–2 minutes. Add cauliflower and vegetable stock, increase heat to medium-high, and cook until cauliflower is soft. Remove pot from heat, add potatoes, milk, and 1/2 teaspoon salt. Using an immersion blender (or transfer soup to regular blender), puree soup until smooth and creamy. To serve, ladle one cup of soup into a bowl and top with cheese, bacon, chives, and roasted broccoli.