Brie tartlets with fresh grape relish

1⁄2 cup thinly sliced seedless red grapes or whole champagne grapes;

1 tablespoon finely chopped scallions (white and tender green parts);

2 teaspoons highquality balsamic vinegar;

11⁄2 teaspoons very finely chopped fresh rosemary;

1⁄4 teaspoon kosher salt;

1⁄4 teaspoon ground black pepper;

24 (11⁄2-inch) baked pastry shells;

3 ounces high-quality Brie or other similar cheese, rind removed;

1⁄4 cup coarsely chopped walnuts, lightly toasted.

Preheat the oven to 300°F.
To make the relish, stir together the grapes, scallions, vinegar, rosemary, salt, and pepper in a small bowl.
Arrange the pastry shells on a baking sheet. Place 1 teaspoon of the cheese and 1⁄2 teaspoon of the walnuts in each shell. Bake only until the cheese begins to melt, about 5 minutes; do not overbake.
Top each tartlet with about 1⁄2 teaspoon of the relish. Serve soon. They taste best slightly warm but are fine at room temperature.
Make-ahead note: You can make the grape relish up to 1 day ahead. Store the relish covered and refrigerated. You can fill the pastry shells with walnuts and cheese up to 6 hours ahead. Store covered and refrigerated.