Place an opened can of coconut cream or milk in the fridge overnight (the milk may require up to 24 hours to thicken). The cream/milk will thicken on the top of the can.
Scoop the thicken cream from the can, discarding the watery remains, into a heatproof glass bowl. Measure the amount of cream that is used.
1/2 fill a saucepan with water and bring to a boil. Reduce the temperature to medium and allow the water to simmer.
Place the cream bowl over the saucepan of water (a double basin) making sure the bowl isn't touching the water. Place a candy thermometer in the cream and bring it to 80-85C/176-185F. If you don't have a candy thermometer this the point when the cream is quite warm to the touch and before it starts to boil.
Add the lemon juice. For 1 1/2 cups of cream (which is how much I get from 1 400ml can) 2 teaspoons of lemon juice are required. Alter the lemon juice depending on the amount of cream you have (eg 1 cup cream 1 1/3 teaspoon lemon juice). Stir the lemon juice through.
Maintain the cream temperature at 80-85C/176-185F for 5 minutes. This may require the stove temperature to be altered.
Remove the cream bowl from the saucepan and allow to cool.
Meanwhile, prepare the sieve.
Place a piece of cheesecloth, a tea towel or paper towel over a fine weaved sieve (I used a kitchen strainer) and place the sieve over a bowl.
Pour the cooled cream into the lined sieve and place in the fridge for 24 hours.
After 24 hours the marscarpone cream will be thickened and glossy.
Transfer to a container and keep refrigerated. The marscarpone cream will keep for up to 3-5 days.