Arrange a rack in the middle of the oven and preheat to 350°F/177°C.
Make the rosemary-walnut butter: In a small cast-iron skillet (or saucepan), melt 1 tablespoon unsalted butter over medium heat. Add 1 teaspoon finely chopped rosemary and 2 tablespoons unsalted walnuts, and cook in the butter until they release their aroma and become slightly toasted, about 2 - 3 minutes.Stir in the 1 teaspoon orange zest, then remove from the heat and let cool until lukewarm, but not hot.
Prepare the brie: If using the same pan to bake the brie, transfer the butter to a small bowl and wipe the skillet clean. Alternatively, use a small oven-safe dish, just large enough to hold the brie wheel.With a sharp knife, lightly score the brie rind in a criss-cross pattern. Place into the skillet.
Add the toppings: Evenly layer the brie with ¼ cup fig jam, then top with the rosemary walnut butter. Sprinkle with flaky salt.
Bake: Bake the brie in the oven for 10 - 15 minutes, or until the cheese is nicely melted. To check, press a knife gently against the flesh of the cheese; it should feel soft. Remove from the oven and cool for about 5 minutes before serving in the baking dish alongside crackers, bread, and/or fruit.
Notes
Make-Ahead: Score and top the brie with the jam and butter, then wrap in plastic wrap. Store in the refrigerator for up to 2 days. Just before baking, remove the plastic wrap and bake according to the recipe instructions.Leftovers: Leftover baked brie will last up to 3 days in the refrigerator in an airtight container. Reheat leftovers in a baking dish for 5 - 10 minutes at 350°F/177°C until warmed through.