Preheat oven to 400°F.
Toss carrots, fennel and onion with olive oil and season liberally with salt and pepper. Scatter on a baking sheet with the thyme and roast about 20 minutes in upper third of oven. Add garlic in skins and turn vegetables; roast about 20 minutes more. Remove and cool to room temp.
Peel garlic and add the roasted veggies to a food processor or high-powered blender in batches, puréeing with stock. Add to a soup pot and heat through, use water to thin if soup is too thick. Stir in honey.
For the topping, pulse bread into coarse crumbs in food processor. Heat oil, a turn of the pan, in a medium skillet over medium heat and melt butter into oil. When it foams, add fennel seed and red chili flakes, and swirl a minute. Add breadcrumbs and toast until golden, seasoning with salt and pepper to taste. Add cheese and stir a minute or two more.
Serve soup in shallow bowls topped with a dollop of Mascarpone or crème fraîche to stir in, some of the chopped fronds and some fennel-chili crumbs.