I start by heating my oven to 350°F and lining a small baking dish with parchment paper. Then I unwrap the brie completely and set the whole wheel in the center of the dish. Using a paring knife, I cut a crosshatch pattern about half an inch deep into the top only, being careful not to slice into the sides.
Next, I spoon the jam right over the top of the brie, spreading it out so it reaches close to the edges. I scatter the raw walnut or pecan halves evenly over that layer of jam. This is the fun part where you can really make the flavor your own.
I slide the dish into the oven and bake for 15-18 minutes. I know it's ready when the nuts turn golden-brown and the cheese feels soft when I gently press the top. The whole kitchen smells incredible at this point.
Once it's out of the oven, I let the brie rest for two to three minutes so it firms up just slightly. Then I lift it out by the parchment paper onto a serving board, sprinkle the fresh rosemary on top, and dig in with crackers close by.