Preheat your oven to 325°F (160°C). Arrange the crispy baked ham pieces on a baking sheet in a single layer. Bake for 20–25 minutes, or until golden and crisp. Once done, remove it from the oven, let it cool slightly, and then break the ham into bite-sized pieces for mixing into the Collard Green Gratin.

In a medium skillet, heat 2 tablespoons of olive oil over medium heat. Add the fresh breadcrumbs and toast them for 10–15 minutes, stirring often until they turn golden brown. Once they are nicely browned, remove from heat and mix in thyme, ¼ cup Parmesan, salt, and pepper. Finally, stir in the baked ham pieces and set this crunchy topping aside.

Bring a large pot of salted water to a boil. Add the collard greens and cook them for about 4 minutes, until they are tender and bright green. Drain the greens and immediately plunge them into an ice water bath to stop the cooking process. Once cool, drain again, chop them finely, and squeeze out any excess moisture before adding them to your mixing bowl.

Using the same pot, heat an additional 2 tablespoons of olive oil over medium heat. Add the chopped onion and minced garlic, sautéing for 15–20 minutes until they are soft and golden. Once done, transfer these sautéed aromatics into the bowl with the chopped collard greens, thoroughly combining everything for a well-flavored mixture.

Raise the oven temperature to 400°F (200°C). In a saucepan, melt the butter over medium heat and carefully whisk in the flour. Cook this mixture, called a roux, for roughly 4 minutes until it turns pale brown. Gradually add the milk while constantly whisking, then sprinkle in nutmeg. Bring the mixture to a simmer, cooking for about 5–8 minutes until it thickens, and then fold it into the collard greens and aromatics.

Transfer the creamy collard green mixture into a suitable skillet or pie dish. Evenly spread the toasted breadcrumb topping over the top, ensuring a nice layer to achieve that delightful crunch in the Collard Green Gratin. Place the dish on a baking sheet and bake in the preheated oven for 15–20 minutes, or until the gratin is bubbling and golden brown. Let it cool for a few minutes before serving to enjoy every comforting bite.