In a large skillet, over medium heat, add the bacon and cook until crisp, about 7 minutes. Transfer the bacon to a paper towel-lined plate to drain. Pour off all but 1 tablespoon of the fat from the skillet. Add the onion and cook, stirring, until softened, 3 to 5 minutes. Add the spinach and toss until wilted.
Add the cream and salt and pepper, to taste. Let it bubble over medium heat until the cream is thickened and clinging to the spinach, about 10 minutes. Transfer the spinach to a serving bowl, crumble the bacon over the spinach, stir, and serve.