Melt the butter in a large pot over medium heat. Saute the onion until translucent, about 3-4 minutes, then add the garlic and red pepper flakes, if you’re using them. Cook for another minute or two.
Add the collard greens, tossing to coat in the onion, garlic, and red pepper flakes, seasoning with salt as you go. Pour in the vegetable stock, cover, and bring to a simmer. Cook until greens are tender––about 45 minutes––and serve with hot sauce or pepper sauce, if desired.
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