In a bowl, whisk the cold thickened cream till firm but avoid to overmix it then set aside.
In another bowl, whisk the mascarpone or cream cheese till soft and creamy then add the condensed milk and keep whisking till well combined.
Add the whipped cream to the cream and condensed milk mixture and whisk for few seconds.
Scrape the bottom and the sides of the bowl and whisk again till you see it thickening up.
Always remember that if you whisk it too long, you could break it down and it could separate or become runny.