You can never have too many hor d'oeuvre recipes, so give Onion Tart Head to the store and pick up pepper, egg, pie dough, and a few other things to make it today. To use up the onion you could follow this main course with the Candy Corn Cupcakes as a dessert. It is a good option if you're following a vegetarian diet.
Heat oil in a skillet over medium-high heat.
Add onion, thyme, salt, and pepper; cook 20 minutes, stirring occasionally.
Roll dough out on a parchment paper-lined baking sheet.
Sprinkle feta cheese in center, leaving a 1 1/2-inch border; top with onion.
Sprinkle with Swiss cheese. Fold piecrust border up and over onion mixture, pleating as you go, leaving a 6-inch-wide opening.
Combine egg and 2 tablespoons water; brush over dough.
Bake at 425 for 25 minutes or until golden. Cool for 10 minutes.