1 l (1/4 gallon) whipping cream 15% fat (or 22% fat)
¼ tsp citric acid
Possibly unexpected tools:
2 dry (!) ceramic, glass or enameled saucepans (No metallic pans!)
1 piece of clean linen fabric
Pour whipping cream into the saucepan, and heat at low heating to 75 C (170 F).
Do not overheat!
Dissolve citric acid with 1 tsp water.
Pour this sour liquid into the warm whipping cream.
Stir carefully, continuing very low heating for about 10 minutes.
Place linen folded twice over into the colander, and pour the whipping cream over it tablespoonful at a time. Let the whey drip for about 1 - 1.5 hours (and, ideally, keep it for other dishes).
You will have wait until it reaches the consistency of mild dough to proceed.
Afterwards, place the mix in a dry saucepan, and place it in a refrigerator.
It will thicken.
You will get about 1 lb Mascarpone from 1 liter of whipping cream.