Whip the cream just until it reaches medium peaks - this means that peaks will form but will still flop over. Don't let it go all the way to stiff peaks or it won't incorporate smoothly into the mascarpone. See the diagram in the post above for a visual guide on the stages of whipped cream.
Remove the mascarpone from the fridge and mix it a couple of times just to loosen it up a bit. Add it to a bowl along with the sifted powdered sugar and vanilla extract, then mix everything together just until combined and smooth - mascarpone will split very easily if it is even slightly overmixed.
Gently fold the whipped cream into the mascarpone mixture just until combined. Refrigerate until ready to assemble the tiramisu.
Add a little less than half of the mascarpone cream on top of the ladyfingers layer and spread it out as smoothly as possible.
Notes
Ingredient Notes
Heavy Cream - Use heavy whipping cream (double cream in the UK) with at least 35% fat. Lower-fat creams won't whip up as well and can result in a looser mascarpone cream. As a UK baker writing recipes primarily for a US audience, I test and develop recipes with these ingredient differences in mind. This mascarpone cream works beautifully with both double cream and heavy whipping cream.Mascarpone Cheese - Use full-fat mascarpone. If your brand has excess liquid in it, be sure to drain that off first.