Heat oven to 375F (190C). Grease a 12-cup muffin tin generously with cooking spray, or use a silicone muffin pan - silicone releases cleanly without spray.
Cook sausage in a large skillet over medium-high heat, breaking into small crumbles, until fully browned with no pink remaining - about 6 to 8 minutes. Drain excess fat and let cool for 5 minutes.
In a large bowl, whisk together Bisquick (or flour + baking powder + salt), milk, and eggs until just combined. Stop the moment it comes together - a few lumps are fine. Do NOT over-mix.
Add the cooled sausage and shredded cheddar to the batter. Fold gently with a rubber spatula - 8 to 10 sweeping strokes only. The batter should still look rough and lumpy.
Divide batter evenly among the 12 muffin cups, filling each about 3/4 full. An ice cream scoop works perfectly for even portions.
Bake for 13 to 16 minutes, until the tops are golden-brown and a toothpick inserted in the center comes out clean. Check at 13 minutes.
Let muffins cool in the pan for 5 minutes. Run a butter knife gently around each muffin to release, then lift out. Serve warm.
