Start by preheating your oven to 425 degrees Fahrenheit so it's fully hot by the time your muffins go in. Press one sausage patty firmly into the bottom of each muffin cup, making sure it sits flat. A snug fit here keeps the pancake batter from sliding underneath later.
Slide the muffin tin into the oven and bake the sausage patties alone for about 5 minutes. This step firms them up and renders a little extra fat, which actually helps the pancake batter bond to the sausage as everything finishes baking together.
While the sausage bakes, prepare your pancake mix according to the package instructions, but swap out the water for milk instead. Whisk until the batter is smooth and mostly lump-free, since a smoother batter pours more evenly over each patty.
Pull the tin out of the oven once the sausage has firmed up, then pour the pancake batter directly over each patty. Fill each cup close to the top, since the batter will puff up slightly but won't overflow much during baking.
Return the tin to the oven and bake for another 20 to 25 minutes, or until the tops turn a deep golden brown. You'll know they're ready when a toothpick inserted into the pancake portion comes out clean.
Let the muffins rest in the tin for 2 to 3 minutes once they come out of the oven, since this brief rest makes them far easier to remove. Run a butter knife gently around the edge of each one before lifting them out onto a cooling rack.