HELP How do I make single cream into sour cream?????

[ButtonMoon]

I have bought some single cream and need to make it into soured cream. I think I read somewhere about being able to add lemon juice but how much???

A BBC recipe just has

"For the sour cream
290ml/½ pint double cream
1 lemon, juice only

• stir the lemon juice into the cream".

HTH!

(Can't find anything with single cream but assume proportions would be the same?)