Bring 1 cup of water to a boil, then add ½ cup old-fashioned rolled oats and a pinch of kosher salt. Lower the heat and simmer until the oats are tender and the water has thickened and mostly evaporated.
Turn the heat down to low, and stir ⅓ cup cold water into the oats.
Beat 1 large egg with a whisk until combined, pour into the oatmeal, and whisk vigorously to incorporate. Cook for about 3 minutes until the oatmeal has thickened and is very creamy.
Serve the custard oatmeal with your choice of toppings, including nuts and fruit for a sweet breakfast, or cheese and kimchi for a savory option.
