Combine first 5 ingredients, 2 cups honey mead, and 2 tablespoons salt in a medium saucepan over medium-high heat; bring to a boil. Transfer mixture to a large bowl, and let cool to room temperature. Add goose breasts to marinade, cover, and refrigerate 8 to 12 hours.
Preheat oven to 375°. Drain goose and pat dry with paper towels; discard marinade. Heat olive oil in a large oven-safe skillet over medium-high heat. Add goose breasts, skin sides down, and cook about 6 minutes or until skin is deep golden brown and fat has rendered. Flip goose; cook 1 more minute. Transfer skillet to oven, and roast 10 minutes or until goose is cooked through.
Meanwhile, cook remaining 4 cups honey mead in a medium saucepan over medium-high heat about 15 minutes or until reduced to 1 cup. Stir in butter, chopped thyme, pepper, and remaining 1/2 teaspoon salt. Spoon sauce over cooked goose, and serve with Sautéed Cabbage & Currants and Brûléed Pears.