Put the chicken stock and butter in a medium pot over medium-high heat and bring to a boil. Add the grits, stir, cover and reduce the heat to low. Cook for 15 minutes, then add the cream. Stir and cook for 10 more minutes. Stir in the bacon and jalapenos. Simmer until the grits are done, about 10 minutes more. Stir in the mascarpone and Cheddar.