Pie crust

1. If pie crust is frozen, remove from freezer and allow to thaw at room temperature for about 2 hours before assembling/baking.

Tomatoes

1. Place paper towels under a cooling rack, then place tomato slices on cooling rack. Lightly sprinkle tomato slices with salt and allow them to rest for 15 minutes, then flip and sprinkle again with salt.

Caramelized onions

1. Heat butter in a large cast-iron skillet over medium heat. Add onions slices, then sprinkle with 1/4 tsp salt. Reduce heat to medium-low. Allow to cook, stirring occasionally for about 30-35 minutes. You should hear a gentle sizzle during the entire cooking process. If the sizzle is loud and intense, the heat is too high.
2. During the last 5 minutes of cooking the onions, add the brown sugar and red wine vinegar.

Assemble & bake

1. Preheat oven to 400.
2. Roll the thawed pie dough out and place on a parchment paper-lined baking sheet. Press together any cracks, use a rolling pin to smooth out the dough if necessary.
3. Arrange caramelized onions on pie crust, leaving a 2-3 inch edge of pie crust around the onions (reserve about a tablespoon of caramelized onions to scatter on top after baking). Then arrange tomato slices on top of the onions.
4. Fold up the edges of the pie crust around the tomatoes. Brush the crust with beaten egg if using.
5. Bake for 25-35 minutes, until crust is golden brown. After removing from the oven, scatter reserved caramelized onions on and fresh basil on top.
6. Enjoy!