My great grandmother used this simple 4 ingredient trick to stretch a dollar. We make it every Mother’s Day to honor her and the kids always beg for second helpings.
Once the spaghetti is cooked to your liking and the onions are deeply golden and silky, taste and adjust seasoning with a pinch more salt if needed (especially if you used low-sodium broth).
Turn off the slow cooker, let the pasta sit uncovered for 5 minutes to thicken slightly, then serve the onion spaghetti hot on warm plates, twirling strands so the caramelized onions cling to the pasta.
Variations & Tips
To stay true to the four-ingredient spirit, keep changes minimal and thoughtful. If you prefer, use all water seasoned with 1 teaspoon salt instead of broth; this is closer to what a Depression era cook might have done when stock wasn’t available.
For a slightly richer flavor, brown the butter in a small pan before adding it to the slow cooker, which will give the sauce a nutty depth without adding more ingredients. You can also swap yellow onions for sweet onions if that’s what you have; they’ll cook down a bit faster and taste slightly sweeter.
If you need to hold the dish for a bit before serving, switch the slow cooker to WARM and stir occasionally; add a splash of hot water if it thickens too much. For food safety, keep the slow cooker on HIGH or LOW only within its recommended time range and do not leave cooked pasta at room temperature for more than 2 hours. Refrigerate leftovers in a shallow container within 2 hours of cooking and reheat thoroughly until steaming hot before serving.
