Sauce made from butter and cream flakes/curdles

Question

My sauce recipe (Laurent Tourondel, BLT p 140) called for heavy cream and butter to be set on high heat:

Put the cream and butter over high heat. cook until the butter is melted and browned, about 5 minutes. Stir in the shallot and garlic and cook for another 3 to 4 minutes, until tender.

Everything went well for the first 5 minutes but after adding shallot and garlic and keeping it over high heat for another 2-3 minutes, the sauce started to flake/curdle.

I replaced heavy cream with sour cream.

I had a look at this answer that only gives »alcohol and acidity« as causes for curdling and this one which advises not to overheat crème fraîche lest it will curdle.

Did heat cause my flaking/curdling? If not, what did? And What means »tender« in this context?

Answer 1

Tender means soft and not brown. Sour cream will curdle if the fat content is not high enough (if it is high, it is called creme fraiche, techniquelly) and if you cook it down too much on too hot heat. Next time, use higher fat content and cook on lower heat. Cream, sour cream and creme freche are not really substitutions, not techniquelly and not taste-wise.Mixing butter and sour cream will work, if you take your time and boil down with hardly any or no bubbles.