Heat 1 tbsp oil and 1 tbsp butter over medium heat in a medium heavy-bottomed pot; add carrots and stir with a wooden spoon until well coated. Add 125ml water, 1/2 tsp salt and 1/2 tsp sugar; cover and cook 5 minutes, or until tender. Uncover and cook, stirring occasionally, until water evaporates and carrots are just starting to brown, a few minutes more. Reserve half of the carrots. In a blender, purée other half with 190ml hot water.
Bring the stock to a simmer and keep at a simmer, covered, over low heat.
Heat remaining oil and butter over medium heat in same (unwashed) pot used for carrots. Add onion and cook until translucent, about 3 minutes. Add rice, stirring with a wooden spoon to coat rice with oil, 1 minute. Add wine and cook, stirring, until wine evaporates. Add carrot purée and cook, stirring, until mixture no longer looks soupy.
Add 190ml hot stock, stirring often, until rice absorbs most of the liquid. Repeat process, adding 190ml stock at a time and stirring often till each addition is absorbed before adding the next, until rice is al dente (about 20 minutes; about 250ml stock should be left).
Fold in reserved carrots (save 2 tbsp. for garnish), the mascarpone, half the parmesan, the parsley and thyme. Add up to 250ml stock - 40ml at a time - to loosen the risotto. Season with salt and white pepper to taste.
Sprinkle each bowl of risotto with some of remaining parmesan, remaining 1 tbsp. parsley, and reserved carrots. Serve immediately.