Preheat oven to 400°F. Place red bell peppers, cut side down, on a foil lined baking sheet and roast in the oven for about 30 to 40 minutes, or until the skins become wrinkled and slightly charred.
Place the roasted bell peppers into a plastic zip top bag (or in a bowl, covered with a plate), close and steam the peppers for about 15 minutes. When ready, remove from the plastic bag or bowl, top off the stems, peel off the charred skins and slice into thin strips. (Don’t have the time to prep homemade roasted peppers? Swap in simple canned or jarred roasted red peppers from the supermarket.)
Using a large stockpot or Dutch oven, heat the olive oil over medium-high heat. Add the leeks, potatoes and cauliflower and cook, stirring often, until the vegetables have started to soften, 8 to 10 minutes. Season with salt and pepper and mix one more time.
Pour in the vegetable stock and bring to a boil. Reduce the heat to a low simmer and cook for about 30 minutes, or until the vegetables are tender. Remove from the heat.
Using a sauté pan over medium high heat, heat a glug of olive oil for a minute or so and add in the mushrooms. Sauté the mushrooms until tender, 5 to 6 minutes, and season with some salt.
Using an immersion hand blender or Vitamix blender, puree the soup until smooth (if using a standard blender, puree the soup 2 cups at a time). This is what gives the soup its creaminess without any cream! Add in lactose-free cow’s milk and mix together well. Season with salt and pepper to taste. Serve in bowls and garnish with the sautéed mushrooms, roasted red bell peppers, fresh chives and Parmesan. Mix and enjoy.