Preheat the oven to 375 degrees F. Lightly grease a 24-cup mini muffin tin with cooking spray.
Roll the puff pastry out between two sheets of parchment paper or on a lightly floured counter to about 10-X14-inches. Cut the puff pastry sheet lengthwise into four strips and then crosswise into six strips to make 24 squares.
Gently press each square into the cups of the prepared muffin tin.
Cut the brie into 24 pieces, about 3/4- to 1-inch in size (removing the rind is optional; I like to cut as much off as possible without digging into the cheese). If the brie is too soft to cut easily, use a knife coated in cooking spray to cut and/or freeze the brie for a few minutes.
Press each piece of brie into a round, thick disc shape and place in the bottom of each muffin cup.
Add a teaspoon or so of cranberry sauce on top of each piece of brie followed by a sprinkle of pecans and a pinch of brown sugar and salt.
Place the mini muffin tin on a foil-lined baking sheet to catch any spillovers and bake for 18-20 minutes until the puff pastry is golden and the cheese is sizzling.
Remove from the oven and let cool in the pan for 2-3 minutes. Use a butter knife to gently lift each puff pastry bite from the muffin tin to a platter. Serve warm or at room temperature.
For the homemade cranberry sauce, combine all the ingredients in a small saucepan. Bring to a simmer and cook, stirring often, until the cranberries have burst and softened and the sauce is thick and syrupy (it will thicken more as it cools). Let the sauce cool to room temp before using in the recipe.