Preheat your oven to 350°F (180°C). While it heats, generously grease a 9-inch pie dish or similar-sized baking dish with butter or cooking spray, making sure to coat the bottom and sides evenly. This prevents the quiche from sticking and helps it release cleanly after baking.

While the oven preheats, dice the ham into 1/4-inch pieces, thinly slice the green onion (both white and light green parts), and shred the cheese if using a block. Having everything prepped and ready ensures smooth assembly and prevents the egg mixture from sitting too long before baking. I like to keep the ham pieces consistent in size so they cook evenly throughout the quiche.

In a large mixing bowl, whisk together the room-temperature eggs, heavy cream, salt, and black pepper until well combined and smooth. Room-temperature eggs blend more smoothly and create a silkier texture in the finished quiche. Whisk for about 1-2 minutes until the mixture is uniform and slightly frothy.

Scatter about two-thirds of the diced ham, shredded cheese, and sliced green onion evenly across the bottom of the prepared pie dish. Pour the egg custard mixture from Step 3 over the filling, then sprinkle the remaining ham, cheese, and green onion on top. This layering technique ensures the toppings won't all sink to the bottom—the final layer stays visible and adds a nice finished appearance.

Place the quiche in the preheated 350°F oven and bake for 35-40 minutes. The quiche is done when the top is golden brown and the center is almost firm but still has a slight jiggle when gently shaken—it will continue cooking slightly as it cools. I find the residual heat will finish setting the center perfectly during the resting period, so don't overbake or it will become rubbery.

Remove the quiche from the oven and let it rest at room temperature for 5 minutes. This resting period allows the custard to set completely and makes slicing cleaner. Cut into wedges and serve warm or at room temperature.