Into two separate small bowls, zest and juice the lemons.
In a small bowl, whisk the egg yolks, sugar and salt and set aside.
In a medium sized saucepan, pour the creams and milk, mix with lemon zest and vanilla. Bring to a simmer over medium heat, cover and let steep for 30 minutes. The strain through a fine sieve and return to the saucepan, add the lemon juice at this point.
Reheat the cream to just steaming, then slowly, whisking constantly, whisk half of the cream into the yolk/sugar mixture. Then whisk the yolk mixture back into the cream and set over medium low heat. Continue cooking and stirring until the custard is thick enough to coat the back of a spoon (about 15 minutes).
Cool to room temperature, then cover and refrigerate for 4 hours minimum, but preferably overnight.
Follow your ice cream maker manufacturers instructions to churn your ice cream.
Store in an airtight container in the freezer.