Hope this helps.
During my research for a book of 70's school dinner recipes I hunted high and low for this mock cream recipe. Lots of testing and tasting later here it is. I think it may be a relative of cream filling you are looking for.
Here's how to make it.
Ingredients
5g plain flour (I find 00 works really well),
100 ml milk
50g caster sugar
70g Butter
Vanilla extract
How to …….
1. Mix the flour and a splash of the milk to a paste. Add the rest of the milk to this paste and put into a small saucepan. Heat gently, stirring constantly until the mix boils. Simmer, stirring constantly, for three minutes. Leave to one side to cool.
2. Cream together the butter and sugar. This is best done with an electric hand mixer as you need to cream the butter and sugar until it is no longer grainy and has become very pale.
3. Check the flour and milk mix has cooled.
4. When cooled use the electric hand mixer again to combine the creamed butter and sugar mixture with the flour and milk mix. Add the vanilla extract at this point. Beat together until the mock cream is light and airy. This may take a moment or two.
5. School tarts were always rectangular so make a baking tray shaped jam tart and pipe this onto each square for the full retro effect. 