Preheat oven to 350 degrees. Place muffin liners in a 12-hole muffin tin.
Wash and steam potatoes until just done or slightly underdone, about 10 to 15 minutes; cool immediately. Slice each potato into four rounds; set aside.
Wash and steam spinach until just wilted, about 3 to 5 minutes; cool, drain well, squeeze out any remaining water and set aside.
In a small bowl, combine ricotta cheese, eggs and chives.
Place a middle slice of potato in the bottom of each muffin hole so it lays flat. Top each with a quarter-slice of bacon, 1 heaping tsp ricotta cheese mixture, about 2 Tbsp spinach, about a Tbsp cheese, another bacon quarter, and another heaping tsp ricotta mixture. Finish stacks by placing remaining potato slices on top and sprinkling with a few remaining shreds of cheese.
Bake stacks until fully set and ricotta is cooked through, about 30
to 35 minutes. Cool in muffin tins for about 10 to 15 minutes and then
transfer to racks to continue cooling.