In a large skillet over medium-high heat, add the raw chorizo. Cook the chorizo, breaking it up as it cooks, about 6-8 minutes.
Remove the cooked chorizo to a paper towel-lined plate (to soak up the extra oil, leaving the oil in the skillet.
Lower the heat to medium and add the unsalted butter. When the butter has melted, add the flour. Whisk constantly until the butter and oil has absorbed the flour. Cook the flour for a minute or two, continuing to whisk.
Slowly add the milk, one cup at a time, while whisking constantly to ensure no lumps. Continue whisking until the milk is well incorporated. You may need to use a rubber spatula to scrape the edges of the skillet.
Add the salt, pepper, and crushed red pepper flakes. I like my sausage gravy really pepper-y so I usually add 2 tsp of black pepper (whatever your preference). Add the chorizo back to the gravy and stir.
Let the gravy bubble for a few minutes until it has thickened. Taste, and add more seasoning if needed.
Serve over fresh, warm biscuits. Optional- Top with chopped fresh parsley (or cilantro). Enjoy!!