Homemade double/heavy cream separates after setting in the fridge Good day. I recently made a homemade double cream using 1.5 cups of whole milk and 150 grams of unsalted butter. I followed most recipes I saw online which started with melting the butter so that it becomes liquid and not letting it boil and mixing it with the milk. However, I had several problems as I placed the melted butter in cold milk which lead to the butter forming again which in turn made it difficult for me to mix with a hand mixer. What I did next was I placed the mixture in a saucepan and let it warm over low heat. When the butter turned liquid again and the milk starting to become warm, I took it off the pan and back to my mixing bowl then used a hand mixer for about two and a half minutes. 

When the mixture looked mixed to me, I placed it in a container and placed it in the fridge to set. However, upon returning to it a couple of hours later, the double cream separated, the butter formed at the top part and the milk was at the bottom. 

My question is, can I still turn this disaster of a double cream and make it usable for cooking/baking purposes? Or should I toss it to the bin and start on a new one? (and this time make sure that the milk is in room temp before mixing the two components)
You cannot make double cream by mixing milk and butter, this is wishful thinking. Some recipes which call for heavy cream, e.g. a cream soup, can indeed be made by adding milk and butter in such quantities that the fat ratio becomes similar to double cream, and will be successful. But for all such cases, there is no reason to mix the milk and butter before adding them to the other ingredients, you can step the step which supposedly makes cream. 

A mixture of butter and milk will always be unstable, no matter the temperature at which you added them. You could in theory avoid it by using an emulsifier and a very thorough mixing method (high powered blenders are good here), but the result will have a different taste and somewhat different texture from cream and still won't whip. I've never seen a use case where doing it makes any sense.