In a large saute pan, heat the oil over medium-high heat. Add the tasso and cook, stirring, for 1 minute. Add the shallots and garlic and cook, stirring, for 1 minute. Add the cream and bring to a boil. Lower the heat slightly and simmer until reduced by half, 3 to 4 minutes. Add the green onions, hot sauce, lemon juice, and salt. Add the butter and cook, stirring, until incorporated and thick. Remove from the heat and adjust the seasoning, to taste.