In a large pot, heat a drizzle of olive oil on medium-high until hot. Add the garlic and onion and season with salt and pepper. Cook, stirring occasionally, until slightly softened, about 5 minutes. Add the bell pepper and crushed red pepper flakes and continue to cook until the pepper is softened, 5 minutes.
Add the potato, cauliflower, stock, milk, bay leaf, 1/2 teaspoon kosher salt, cumin, and coriander. Bring to a boil, then reduce to a simmer. Cook, stirring occasionally and mashing a bit with the back of a spoon, 10 to 15 minutes, or until the potato and cauliflower are tender. Turn off the heat. Let cool slightly
Ladle about 2/3 of the vegetable chunks and a little bit of liquid into a blender and blend until smooth (or use an immersion blender and leave some chunkiness un-blended). Be careful! This is hot! Duh. Return the blended soup to the pot; heat over medium and stir to combine, heating everything through.
Serve the soup with black pepper and parmesan on top.