Here's the Photo Tutorial

Heat the oil in the roomy saucepan. Make sure to use a large pot as there will be a large amount of liquid and you'll need to be able to stir without spillage.

For a richer flavor use 2 oz or 100 gm of butter, but for the sake of health, substitute with a good quality olive or rice bran oil.

Once heated, toss in all the flour.

See how the mixture clumps together like small pieces of dough, much like large breadcrumbs.

Scatter over the crumbled stock cubes and add seasoning as suits your taste. Keep stirring to combine into the crumb mixture.

Pour in all the milk then water.

Keep stirring to prevent the dough from sticking to the bottom of the pot and to incorporate it into the liquid.

The mixture is very thin at the start.  Keep the heat on high as you keep combining.

Nothing will happen for a while, but about 10 to 15 minutes later the liquid will suddenly thicken, but keep stirring, though.

As soon as the mixture starts to bubble a little, reduce the heat to low to prevent it boiling. Remember milk products should never be boiled although it can be brought to a low simmer.

Let the white sauce simmer for about 5 minutes to thicken.

Turn the heat off and it's ready to be used in the recipe, like this delicious healthy lasagna recipe.