From WP, this uses frozen puff pastry as the base. It's very simple. I really like puff psatry and need to get used to using it in more recipes.
Ingredients
12 ounces shallots
One 9-by-13 sheet frozen puff pastry (preferably Dufour brand; may substitute Pepperidge Farm; see OVERVIEW), thawed
1/4 cup Dijon mustard
4 ounces aged cheddar (may substitute vegan cheddar), grated
Leaves from 3 stems fresh thyme
Freshly ground black pepper
Instructions
1. Preheat the oven to 400 degrees.
2. 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.
3. 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.
4. 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.