Set the oven to 400°F and let it preheat for 10 to 15 minutes while you work. Unfold the 2 thawed but chilled all-butter puff pastry sheets. Cut each sheet into 9 squares with a sharp knife or pastry wheel. You'll have 18 pieces in all. Then cut the 6 ounces of French Brie into 18 small cubes that measure about 3/4 inch across. Leave the rind on because it helps the cheese hold its shape before it melts. Keep the cut pastry cold while you finish with the cheese. Next, check the pastry edges. They should look pale and firm rather than greasy or stretched. If the sheets turn soft, chill them for 10 minutes before moving on. Warm dough won't puff as well. Cold pastry keeps its butter layers apart for a crisp rise.

Brush the 18 wells of a mini muffin tin with 1 teaspoon of extra virgin olive oil. Use a pastry brush to coat the bottoms and sides with a thin film. Then place one cold pastry square into each well. Press the center down with your fingers and ease the dough into the corners. Leave the four pastry points sticking above the rim. Don't flatten the sides too hard. Work for about 4 to 5 minutes so the dough stays firm and keeps its thin layers. Now you'll see 18 small pastry cups with pale centers and uneven pointed corners. They should sit below the rim in the middle but stand a bit taller at the edges. Thick folded bottoms can stay doughy. Gentle pressure leaves room for the pastry to rise.

Place one cube of French Brie into the center of each of the 18 pastry cups. Then spoon the 1/2 cup of thick whole berry cranberry sauce over the cheese. Use about 1 1/3 teaspoons per cup and leave the pastry corners exposed. Next, sprinkle the 1/4 cup of chopped pecans across all 18 cups. Gently press the pieces into the sauce so they stay in place as the filling warms. This part takes 4 to 5 minutes. Don't pack the filling down or force it over the pastry edges. The cups should now show white Brie beneath small mounds of deep red cranberry sauce. Brown pecan pieces sit partly inside the fruit topping. If the sauce spills over the rims, it may burn as it bakes. Leave space so the filling can bubble without leaking.

Slide the filled mini muffin tin onto the center rack of the fully preheated 400°F oven. Bake for 17 to 20 minutes and start checking at minute 15. The pastry corners should rise and turn golden brown while the cheese softens beneath the fruit topping. You'll see the cranberry sauce begin to bubble around some of the pecan pieces. Keep the tin level when you move it. Don't pull the bites out while the lower edges still look pale because those layers may stay soft. At about minute 18, the pastry should look puffed with crisp amber tips and lighter golden sides. The Brie will be glossy and soft. (I've found that overfilling the cups leaves a sticky mess and hides the crisp edges.) Take them out before the exposed points turn dark brown. Strong heat crisps the layers before the filling can soak them.

Let the baked bites rest in the tin for 5 minutes after they leave the 400°F oven. Then gently lift each one from the edge and move it to a white serving plate. You should have 18 small pastries with crisp corners and soft cheese centers. Sprinkle the 1 teaspoon of finely chopped fresh rosemary over the tops. For a closer look at the layers, cut one bite in half and place the pieces beside each other. Serve the rest whole while they're still warm. Finally, look for a lightly set cranberry topping and cheese that's soft enough to stretch a little when you cut it. The pastry should hold its shape. Lift too soon and the filling may spill. A short rest lets the hot cheese settle without softening the crust.