In a large sauté pan or pot over medium-high heat, melt 1 tbsp. butter. Add sausage and cook, stirring to break into bits, until sausage is cooked through and starting to brown, 3 to 5 minutes.
Add shallot and garlic. Stir until fragrant, 1 minute. Add wine, increase heat to high, and cook until reduced by half, 3 minutes. Reduce heat to medium and stir in remaining butter and the lemon juice.
Add mussels, cover, and increase heat to high. Cook, stirring occasionally, until mussels are open, about 4 minutes. Stir in thyme and pepper. Divide mussels among 12 plates, along with some of the sauce from bottom of pan. Serve immediately.
Note: Nutritional analysis is per serving.