Lightly grease a 24-cup mini muffin tin with nonstick cooking spray and set aside. Preheat the oven to 375 degrees F (for darker coated pans, consider reducing the temperature to 350 degrees).
Dust the counter with a light coating of flour and gently press the sheet of puff pastry out with your hands until it is about 12X12. You aren't really thinning it out as much as getting it into an even thickness throughout and flattening just slightly.
Using a knife or pizza wheel, cut the puff pastry into 25 equal pieces (five strips one way, five strips the other way). Press one square lightly into each muffin cup. You'll have one leftover square - toss or bake on it's own.
Bake the puff pastry for about 8-9 minutes until lightly golden and puffed up.
Remove from the oven and using the rounded, blunt edge of a spoon or spatula (or your finger), press the pastry down in the middle so it is no longer puffed up.
Cut the Brie into 24 1/2-inch or so cubes. If you're working with the rounded edge of a wheel of cheese, combine two smaller pieces, if needed.
Divide the raspberry jam evenly among the pastry cups - lightly warm the jam if it is too thick to drizzle in evenly. Place a piece of Brie on top of the jam.
Mix together the brown sugar and Dijon and sprinkle evenly over the cheese. Return to the oven for about 4-6 minutes to let the cheese melt (watch carefully so the puff pastry doesn't burn).
Serve immediately (these are divine warm but we love them at room temperature too).