Adjust racks to top and middle positions and preheat oven to 425 degrees. Wash and dry produce.

Cut potatoes into ½-inch-thick wedges. Halve, peel, and thinly slice shallot.

Toss potatoes on a baking sheet with a large drizzle of oil, half the garlic powder (you’ll use the rest in the next step), salt, and pepper.

Roast on top rack until browned and tender, 20-25 minutes.

Heat a drizzle of oil in a medium pan over medium heat. Add shallot and cook, stirring, until softened and lightly browned, 2-3 minutes.

Add mustard, half the cream sauce base (you’ll use the rest in the next step), remaining garlic powder, and 1 tsp water (2 tsp for 4 servings); cook until thickened, 30 seconds. 

When potatoes have five minutes left, arrange half the bread slices on a second baking sheet. Top with as much ham as you like; spread with shallot béchamel. Sprinkle with half the gouda.

Place remaining bread slices on top and spread with remaining cream sauce base. Sprinkle with remaining gouda.

Bake on middle rack until cheese melts and bread is toasted, 5-6 minutes. 

Set oven to high broil (remove potatoes from the oven first!); broil sandwiches on middle rack until tops are golden brown, 2-3 minutes. TIP: Watch carefully to avoid burning!

In a large bowl, whisk together half the balsamic glaze and a drizzle of olive oil (all the balsamic glaze and a large drizzle of olive oil for 4 servings); season with salt and pepper.

Add mixed greens to bowl with dressing and toss to coat.

Divide sandwiches, potato wedges, and salad between plates and serve.