Heat the oven to 375°F. Bring a large pot of water to a boil, and set out an 8-inch square baking dish.

Cook the elbow macaroni 2 minutes less than the package directions, until just tender but firm in the center. Drain well.

Pat the chicken dry and season with half the salt and pepper. Heat the olive oil in a 12-inch skillet over medium-high heat. Brown the chicken in one layer, turning once, until the thickest piece reaches 160°F, about 5 to 6 minutes. Transfer to a plate.

Reduce the skillet heat to medium. Add 2 teaspoons of the butter and the onion; cook for 3 to 4 minutes until softened. Add the garlic and stir for 30 seconds.

Stir in the flour and cook for 1 minute. Gradually whisk in the milk and broth; simmer for 2 to 3 minutes until the sauce coats a spoon. Remove from the heat.

Whisk in the Dijon, thyme, remaining salt and pepper, and Swiss cheese until smooth. Do not let the sauce boil after adding the cheese.

Fold in the macaroni, chicken, and ham. Melt the remaining butter, toss it with the panko, and scatter the crumbs over the casserole.

Bake for 18 to 20 minutes, until the edges bubble and the crumbs are browned. Rest for 5 minutes before serving.