Prepare the pie crust according to instructions. Let it chill in the fridge for at least 30 minutes before using. On a lightly floured surface, roll it out to at least 12 inches in diameter. Transfer it to a parchment-lined half sheet pan and transfer it to the fridge to chill.

Thinly slice the onions.

Set a large sauté pan over medium heat and add the 2 tablespoons of butter and ¼ cup of olive oil. When the butter has melted, add the onions and stir to coat them in the fat. Season with 1 teaspoon of salt.

Continue to cook the onions, stirring occasionally, for 45-50 minutes, or until they are nearly half the size and golden brown. They are now in the beginning stages of caramelization.

Add the chopped rosemary, thyme leaves and another teaspoon of salt to the onions. Grate in three garlic cloves and cook for 2-3 minutes or until the garlic is no longer raw.

Turn off the heat and add the sour cream. Stir to combine.

Position a rack to the center of the oven and preheat to 375°F.

Remove the crust from the fridge and spread the onions into a circle in the center of the crust, about 9 inches wide. Fold the edges of the crust over the onions. Let this chill in the fridge while the oven finishes preheating.

Whisk together one egg and brush it on the edges of the crust right before baking.

Bake for 45-50 minutes, or until the onions are a deep brown and the crust is golden. Serve warm!