Preheat oven to 190 °C (375 °F) with the rack in the top position.
Add all ingredients to a large bowl and mix together until fully incorporated.
Grease a muffin tin with non-stick vegetable oil spray and distribute the mixture among each of the 12 cups, pressing down slightly. The cups should be filled to about 1/3 from the top.
Bake for 25 minutes, then increase the heat to 220 °C (425 °F) and continue baking for about 5 minutes.
Let cool for approximately 5 minutes, then carefully remove the hash browns from the muffin tin with the tip of a knife. Serve hot, topped with sour cream and chopped chives.