In a heavy-bottomed saucepan, combine milk, water, and salt. Warm gently over medium-low heat until steaming but not boiling.
Slowly stir in the oats, reducing heat to low.
Simmer gently for 15–20 minutes, stirring occasionally to prevent sticking, until soft and creamy. (If it thickens too much, add a splash of hot water or milk.)
Pour onto shallow plates or into bowls.
Serve warm with a spoonful of sugar, a drizzle of treacle, and cold milk poured gently over the top.
