1. For the mascarpone: in the bowl of a stand mixer with the paddle attachment, beat the mascarpone until smooth and creamy.
2. For the eggs: separate the egg yolks. Set the egg whites aside. In a double broiler, whisk the egg yolks with the sugar until foamy, about 4-5 minutes. Pour into the mascarpone cream, and beat until combined.
3. Add the heavy cream to the mascarpone mixture and beat until incorporated, about 5 minutes. Transfer to a bowl.
4. In the bowl of the cleaned stand mixer, whisk the egg whites and lemon until stiff peaks form, about 5 minutes. Fold into the mascarpone mixture.
5. For the ladyfingers: in a shallow bowl, whisk together the espresso and rum. Dip one ladyfinger at a time, flipping it so both sides get soaked. Repeat as you assemble the tiramisu.

Assembly:

1. Spread mascarpone cream evenly over bottom of your 11″ baking dish. Arrange dipped ladyfingers on top, without leaving any empty spots. Follow by another layer of mascarpone cream, (using an angled spatula to spread evenly) and another layer of mascarpone cream.
2. Add remaining mascarpone cream using a piping bag (no piping tip needed). This step is optional, you can simply spread the mascarpone on top. Cover with plastic wrap and refrigerate for at least 4 hours.
3. Dust cocoa powder right before serving. Keep leftovers refrigerated for up to 2 days.
4. Enjoy!