Melt the butter in a 3-quart or larger saucepan over medium-high heat. Add the flour (or starch) and whisk until all flour is incorporated.
Add the non-dairy milk and broth and whisk until it becomes bubbly. Continue whisking as it boils until the mixture starts to thicken, about 5 minutes. Keep in mind, it will thicken quite a bit more after all the remaining ingredients are added.
Remove the pan from the heat and add the nutritional yeast flakes, vegetable bouillon, and paprika. Once combined, whisk in the vegan cheese.
Note: You may need to place the pan back over low heat for the cheese to completely melt. It may take several minutes of whisking to become smooth.
Carefully taste and add more cheese for a cheesier flavor, and add salt and pepper to taste. Cover and set sauce aside for now.
Preheat your oven to 350°F (approx. 177°C). Grease a 9-x-13-in. (23-x-33-cm) or other 3-quart baking dish with butter and set aside for now.
Cook the elbow pasta in salted boiling water according to the package directions. Drain well and add the pasta to the pot containing the sauce. Stir well to coat all the macaroni noodles. Add salt to taste.
Pour the mac and cheese into the prepared baking dish and smooth over the surface.
In a small bowl, stir together the first six ingredients for the topping. Add the melted butter and stir again. Sprinkle this mixture evenly over the surface of the mac and cheese.
Bake for 25–30 minutes, or until lightly golden brown around the edges. Let the mac and cheese rest at least 5 minutes before serving.