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)

Also, there are no tags for double and heavy cream?