Preheat the oven to 400 degrees Fahrenheit. Grease a 9×9 square baking dish or 9×13 baking dish with cooking spray and set aside.

Add 1 tablespoon of olive oil to a medium skillet over medium heat. Add the chopped onion, garlic and ½ teaspoon of salt. Cook the onion until softened and translucent, stirring occasionally. 

While the onion is cooking, add the frozen hashbrowns to a large bowl. Try to break up the pieces the best you can. I like to hit the package on the counter a few times to break up the larger chunks. When the onions are done, add them to the large bowl with the potatoes.

Place the skillet back onto the stove to make the roux. Melt the butter over medium heat. Whisk in the flour until all the butter has been absorbed. Slowly pour in the vegetable broth, whisking constantly until you have no flour chunks left. Add the mayonnaise, sour cream/yogurt, 1 teaspoon salt, nutritional yeast, and a pinch of pepper and continue to whisk until the mixture starts to thicken and bubble.

Pour the gravy over the potatoes and onions and stir well, covering the potatoes completely. Spoon the potatoes in the baking dish. Sift about 1 teaspoon of paprika on top of the potatoes, cover with aluminum foil and bake in the oven for 50 minutes.

For the last 5 minutes, remove the foil, turn the oven up to broil and broil the potatoes for 3-5 minutes to get the top golden brown and slightly crispy, watching carefully so it doesn’t burn. Allow the potato casserole to set up for about 15 minutes and serve.