BRING ½ cup water to boil in a large pan with salt and lemon zest.
ADD pasta to boiling water and allow to cook. If water evaporates, add more as needed. Once pasta is cooked through, drain any excess water - ideally there will be none leftover - but leave pasta in the pot.
ADD the sugar and butter and let cook for 8 minutes on medium heat.
MIX egg yolks, port wine and 3 tablespoons of water in a separate bowl.
REDUCE heat to low and slowly add egg mixture to the pasta. Stir well.