We caramelize red onion wedges over low heat until sweet, tender, and translucent for a stained glass effect on the finished tart. Don’t worry if the wedges start to fall apart in the skillet; you want a mix of both individual onion petals and wedges for the filling. This is a case where the most beautiful result comes from the least effort: instead of arranging each onion piece, simply pour the whole mixture into the cake pan and smooth into an even layer.
How to Make It
Preheat oven to 400°F.
Heat oil in a large skillet over medium-low. Add salt, pepper, and onions; sauté 15 minutes or until onions are lightly browned. Add sugar, vinegar, and chopped thyme; cook 5 minutes or until liquid evaporates. Remove pan from heat; cool slightly.
Roll pie dough into a 12-inch circle on a lightly floured surface. Place thyme sprigs in bottom of a 9-inch cake pan. Spread onion mixture in bottom of pan in a single layer. Drape dough over pan, folding edges underneath. Prick surface liberally with a fork. Bake at 400°F for 20 minutes. Reduce oven temperature to 350°F (leave pan in oven); bake at 350°F for 15 minutes or until dough is browned and crisp. Remove pan from oven; cool 15 minutes. Carefully invert tart onto a serving plate; cut into 8 wedges.
