For the sausage: Combine pork, garlic, onion powder, sage, thyme and oil in a large bowl and season with salt and pepper. Cover and refrigerate for at least 30 minutes to allow the flavors to meld. Mixture can be prepared 8 hours in advance and refrigerated.
For the gravy: Put milk in a small saucepan and bring to a simmer over medium heat. Melt the butter in a small saucepan over medium heat, whisk in the flour and cook for 1 minute, do not allow the flour to color. Slowly whisk in the warm milk, increase the heat to high and continue whisking until the sauce begins to thicken and the raw taste of the flour has been cooked out, about 5 minutes. Season with salt and pepper. Keep warm.
Form the sausage mixture into 8 patties. Heat a large, nonstick pan over high heat and cook the patties until golden brown on both sides and just cooked through, about 5 minutes per side.
Slice each biscuit in half, put a sausage patty on the bottom of each biscuit, drizzle with the gravy and replace the tops. Serve 2 sausage biscuits per person.