I don't remember anymore where I got the recipe, but I do remember that it called for white wine vinegar, which I didn't have, but I did have white rice wine vinegar, so that is what I used. Here's my method:
10 cups raw milk cream
About 1/2 cup white rice wine vinegar
Warm cream slowly in double boiler to 190 degrees Fahrenheit, stirring occasionally.
Starting with 1/4 cup vinegar, stir it in until cream starts to curdle. You may need to use more vinegar. Once the cream has curdled and is thick, remove from heat and allow to stand for 15 minutes.
Ladle into cheesecloth-lined colander set over another kettle. Allow curds to cool to room temperature, then refrigerate to continue draining and firm up.
When done draining, knead mascarpone and transfer to airtight container. Use or freeze within three days. My yield was 3 3/4 cups of very thick mascarpone.
Note: I tried to use the whey to make ricotta, but it turned out very grainy/not good at all.