Put the water, milk, the salt and the oat flakes in a saucepan. Bring the mixture to the boil once and then simmer gently for about 10 minutes, stirring occasionally, or until it thickens a little. The porridge does not have to have reached the desired consistency at this point, but should still be a little too liquid. It will continue to swell and the cookies will still absorb quite a bit of liquid.
Crumble the biscuits and add them to the porridge with the raspberries. Tip: The crumbs should be about the size of raspberries, but you can also proceed as you wish.
Set the saucepan aside and let the porridge steep for another 5 minutes.
Now divide between 2 bowls and garnish with more raspberries and cookie pieces if necessary.