Serves 3
12 ounces shallots
One 9-by-13 sheet frozen puff pastry, thawed
1/4 cup Dijon mustard
4 ounces aged cheddar, grated
Leaves from 3 stems fresh thyme
Freshly ground black pepper
Preheat the oven to 400 degrees.
Trim the stem end off each shallot, cut each in half lengthwise, and peel. (The shallots are easier to peel after cutting in half.) Cut each half in half lengthwise again.
Lay out the puff pastry on a baking sheet lined with parchment paper, and spread on the mustard, leaving a 1-inch border around the edge. Arrange the shallot slices over the top, then scatter on the cheddar, thyme and pepper.
Bake until the pastry has puffed and the tart is deeply browned, 25 to 30 minutes. Use the parchment paper to transfer the tart to a cutting board to cool. Serve warm or at room temperature.