Select the Sauté setting and heat the oil, butter, shallot, and garlic for about 4 minutes, until the butter is melted, the shallots are softened, and the garlic is bubbling but not browned. Add the cherry tomatoes, thyme, and salt and sauté for about 2 more minutes, until the tomatoes are slightly softened. Add the wine, bring to a simmer, and cook for about 3 minutes, until most of the wine has evaporated. Pour in the stock and bring to a simmer. Add the mussels to the pot, discarding any that do not close to the touch, and stir to coat them in the cooking liquid.