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