Preheat the oven to 425F.

For a homemade pie crust, lightly flour your work surface and roll the dough to about ⅛-inch thick. Fit it into a 9-inch pie dish, leaving a ¾-inch overhang.

Fold the overhang so the crust edge stands tall, then crimp as desired. Line with a piece of parchment paper, fill with pie weights, and blind bake for 5-10 minutes.

If using a store-bought crust, thaw according to package directions and pre-bake in the same way.

Reduce oven temperature to 325F.

Heat a small pan over medium heat then add olive oil and cook onion for 5-10 minutes. Remove from heat and set aside.

In a medium bowl, whisk together eggs, heavy cream, and sea salt until combined, then set aside.

Spread onion evenly on the bottom of the pie crust, then layer the rest of the quiche.

Add half the cheese and ham on top of the onion, pour the egg mixture then layer the remaining half of cheese and ham. If needed, get a fork and lightly press down the ingredients so they are mostly under the egg mixture.

Bake in preheated oven at 325F for about 45 minutes. The center should be set and lightly golden.