In a metal bowl placed over a saucepan of an inch of simmering water, whisk together the egg yolks, powdered erythritol, and vanilla paste.  Whisk constantly until thickened.  When you can draw a number 8 with the thickened mixture, it's ready. DO NOT overcook!

Remove from the heat and let cool for 30 minutes.

Whisk in the mascarpone, then whisk in the yogurt.

Line a 9×5″ loaf pan with two layers of plastic wrap so that there is an overhang.  Make sure to press the plastic into the pan so that the entire pan is coated.

In a shallow dish, add the espresso and rum.  Dunk both sides of a ladyfinger in the mixture (don't let it soak too long otherwise they'll absorb too much and get mushy or even disintegrate) and place it inside the loaf pan.  Do this until you have an entire layer of ladyfingers.

Scoop ⅓ of the mascarpone filling over the ladyfingers and spread it out.

Dunk the ladyfingers in the espresso/rum mixture and line them over the mascarpone filling.

Repeat twice, then top it off with a final layer of dunked ladyfingers.  Tightly cover with plastic wrap and refrigerate overnight.

Remove the plastic wrap and flip the loaf pan onto a serving dish.  Gently remove the loaf pan and carefully peel the plastic wrap off the Tiramisu.  Dust with the cocoa powder, then slice and serve!