Step 1

Heat the oil in a medium frying pan over medium-high heat until shimmering. Add the sausage and cook, breaking up the meat into small pieces with a wooden spoon, until browned and cooked through, about 5 minutes. Add the spinach and cook until wilted, about 2 minutes. Remove from the heat and set aside to cool to room temperature, about 15 minutes.

Step 2

Meanwhile, arrange a rack in the middle of the oven and heat to 375°F. Coat the wells of a standard 12-well muffin pan generously with cooking spray; set aside. Whisk the flour, baking powder, baking soda, salt, and pepper in a large bowl and set aside. Melt the butter and place in a medium bowl to cool to room temperature.

Step 3

Add the buttermilk and eggs to the butter and whisk until combined. Pour the buttermilk mixture into the flour mixture and mix with a wooden spoon or rubber spatula until just combined; some lumps are fine. Add the sausage mixture, sprinkle with the cheese and apple, and fold until just combined. Divide the batter among the muffin wells; they will be very full. Sprinkle with the chives.

Step 4

Bake until the tops just begin to brown and a toothpick inserted in the center of a muffin comes out clean, 20 to 25 minutes. Place the pan on a wire rack and cool for 5 minutes. Run a thin knife around each muffin to loosen, then transfer to the rack. Serve warm or at room temperature.