Heat oven to 450 F with a rack in the middle position. In a 9x13 inch baking pan, mix the oil and tomato paste. Add the tomatoes, garlic, pepper flakes, thyme and 1/2 tsp salt. Roast until the tomatoes have softened and begin to char, 35-40 minutes, stirring once halfway through. Remove and discard the thyme, set the tomatoes aside.
In a large skillet over medium-high melt the butter. Add the shallots and stir for 2-3 minutes until tender.
Add the risotto rice and 1/2 tsp salt, then cook, stirring constantly, until the rice grains are translucent at the edges, 2-3 minutes. Add the sherry and cook, stirring until evaporated.
Add 2.5 cups of boiling water and bring to a boil, then reduce to medium and cook, stirring often until the grains are almost tender but still firm at the centre, 8-10 minutes.
Add 1 cup of the remaining boiling water and cook, stirring often and briskly, until the rice is al dente, 5-7 minutes. The risotto should be loose but not soupy.
Off heat, stir in the tomatoes with juice, basil and parmesan cheese. Taste and season with salt and pepper.
Serve immediately topped with bocconcini cheese.