To make the sauce:In a heavy small saucepan, melt the butter over medium heat.
Add the flour and stir constantly for 1 minute.
Gradually add the milk, whisking constantly.
Add the nutmeg.
Whisk over medium heat until the mixture thickens to sauce consistency and is smooth, about 6 minutes.
Stir in the salt and pepper.
To make the pizza:Preheat the oven to 450 degrees.
Oil a heavy, non-stick 16-by-10-inch baking sheet with olive oil.
Using your fingers, spread the dough over the prepared baking sheet into a rectangle shape.
Spoon the sauce on top and spread evenly leaving a 1-inch border around the dough.
Sprinkle the mozzarella cheese on top.
Toss the pot roast with the sauce to moisten slightly.
Divided the meat evenly over the top.
Sprinkle with Parmesan cheese.
Bake for 15 minutes.
Remove the baking sheet from the oven and add the kale in an even layer on top of leftover pot roast.
Drizzle with olive oil and sprinkle with salt.
Bake for 8 minutes longer until the kale is crispy.
Cut into squares and serve.