Fry bacon strips until crispy and set aside. Reserve 2 tablespoons of bacon grease for sautéing diced onions. Into the skillet over med-high heat add the two tablespoons of bacon grease, when the grease is hot add diced onions and sauté until the onions are translucent, add a pinch of sea salt and a turn or two of black peppercorns. Set aside. Chop fresh parsley, set aside. Leave the skin on but cut away any bad spots or eyes, quarter potatoes and place them into a large stockpot. Sprinkle a tablespoon of salt over potatoes and fill a pot with tepid water until potatoes are covered. Set stockpot over high-heat and cook until potatoes are fork tender. Strain water from potatoes and return to stockpot. Add spinach to potatoes and cover with a tight-fitting lid over med-low heat. The heat will wilt the spinach. After 10 minutes remove the lid from the stockpot and roughly smash the potatoes and spinach together. Add heavy cream, salted butter, garlic, and sautéed onions. Mix until the ingredients are incorporated. Add sea salt and freshly cracked black peppercorns to taste. Spoon potatoes into a serving dish and crumble crispy thick-cut bacon over the potatoes, add chopped parsley. Serve.