Preheat your oven to 375°F while you get everything else ready. Lightly grease a mini muffin tin with non-stick spray or softened butter so the bites release easily later. This small step matters more than people think, because sticky pastry can tear and ruin that pretty golden shape you're going for.
On a lightly floured surface, unroll one sheet of thawed puff pastry and gently roll it out just slightly larger than its original size. Using a sharp knife or pizza cutter, slice it into 12 even squares, then repeat with the second sheet. You should end up with 24 squares total for your mini muffin tin.
Press one square of puff pastry into each cavity of your mini muffin tin, pushing it gently up the sides to form a little cup shape. Don't worry about perfect corners poking out, that rustic look actually bakes up beautifully golden and crisp around the edges.
Cut your brie into small cubes, removing the rind if you prefer a smoother bite, and place one cube into each pastry cup. Spoon about a teaspoon of cranberry sauce directly over the cheese in every cup, letting it sit right on top.
Sprinkle a few chopped pecans over each filled cup for crunch and visual appeal. Brush the exposed edges of the puff pastry with your beaten egg wash, which helps them turn that irresistible deep golden color in the oven.
Slide the tray into your preheated oven and bake for 15-18 minutes, watching for the pastry edges to puff up and turn golden brown. The brie should look soft and just slightly melted, not fully liquid, so it holds its shape when you lift each bite out.
Let the bites rest in the tin for 3-5 minutes before transferring them to a wire rack, which keeps the bottoms crisp instead of steamy. Finish with a little fresh rosemary or thyme sprinkled over the top right before serving for a festive touch.