Place brie on a rimmed baking sheet or a 5-inch cast iron skillet. Place into oven and bake until softened, about 12-15 minutes; let cool 5 minutes.
Spread pecans in a single layer on a clean baking sheet. Place into oven and bake until toasted and fragrant, about 6-8 minutes; set aside.
In a small saucepan over medium heat, combine maple syrup, rosemary, 1/4 teaspoon salt and 1/2 teaspoon pepper. Bring to a boil; reduce heat and simmer, stirring occasionally, until foamy, about 1-2 minutes. Stir in pecans.
Serve brie warm topped with maple syrup mixture; serve with crackers or baguette.