One 12-cup nonstick muffin pan, each cup about 1/2-cup capacity, or a 12-cup popover pan, each cup about 1/2-cup capacity
Place an oven rack in the center of the oven and preheat to 400 degrees F. Butter the muffin cups.
Heat the oil over medium heat in a medium nonstick skillet. Add the sausage and break it into 1/4-to-1/2-inch pieces using a wooden spoon. Cook until brown and cooked through, about 6 minutes. Add the garlic and cook until aromatic, about 30 seconds. Spoon about 1 1/2 tablespoons sausage into each muffin cup. Sprinkle the cheese on top of the sausage.
Blend the eggs in a blender until frothy, about 15 seconds. Add the milk, flour, green onions, basil, salt and pepper. Blend until just incorporated. Pour the batter into the muffin cups, filling each cup to just below the rim. Bake, without opening the oven door, until puffed and golden, about 35 minutes.
Place the popovers on a platter and drizzle with maple syrup.