Mascarpone (often mispronounced as "marscapone") offers a rich, creamy, almost buttery flavour to dishes such as tiramisu. It can be difficult to find, however, and is often relatively expensive compared to other, more common foods such as cream cheese. While you will not obtain quite the same flavour from cream cheese as from mascarpone, you can successfully use it as a substitute. Plain cream cheese works fairly well, but blending it with other ingredients can make an even better replacement for mascarpone.
Remove the cream cheese from the refrigerator and allow it to warm to room temperature. Then stir and smash it thoroughly with a fork to soften it. This will help make its consistency more similar to that of mascarpone and will make it easier to mix the cream cheese with another ingredient, if you so choose.
Mix your cream cheese with heavy whipping cream or sour cream if you wish. If you use sour cream, add up to an equal amount of sour cream to the cream cheese (though you can use significantly less if you wish). When using heavy whipping cream, use up to 1/4 cup per 227gr. of cream cheese. Mix thoroughly to completely blend the sour cream or whipping cream with the cream cheese.
Use your cream cheese --- either plain or mixed --- exactly as you would have used mascarpone. The flavour and texture will be slightly different than that of mascarpone, but similar enough that it will not adversely affect most recipes.