Preheat your oven to 400°F (200°C).

Cook the bacon in a skillet over medium-high heat until it's perfectly crisp. Once cooked, drain it on paper towels and set aside to cool.

Melt butter in the same skillet with the bacon drippings. Add the sweet yellow onions and ¼ teaspoon of salt; sauté for about 18 minutes—cover for the first 5, then uncover for another 10—until the onions are soft and golden brown.

Cool the caramelized onions slightly as you prepare the tart crust.

Prepare your tart pan by spraying it with nonstick cooking spray. Place the pie crust in the pan, gently pressing it into shape, and prick the bottom with a fork to avoid bubbling.

Parbake the crust with foil and weights for 14-16 minutes until dry and just starting to turn golden. Carefully remove the foil and weights after baking.

Whisk together the large eggs and sour cream in a medium bowl until smooth. Then, mix in the crisped bacon, caramelized onions, fresh herbs, the remaining salt, pepper, and nutmeg for a flavorful filling.

Pour the filling into your prepared crust and bake for 25-30 minutes until set and golden-brown.

Cool the tart for about 10-15 minutes. Slice and then serve warm or at room temperature.