In a medium saucepan, combine milk, cream, buttermilk and sugar. Heat on low until sides of pan are slightly bubbly and warm, but not boiling. Add 1/4 cup of the milk mixture to the egg yolks and stir quickly, keep adding small amounts of liquid to the eggs until it it the same temperature as what is in the saucepan. Add egg yolk mixture to the saucepan and continue to heat until you can coat the back of a spoon. Do not boil.
Chill milk mixture and jarred lemon curd overnight.
Add custard to the ice cream maker and begin churning. Add cold lemon curd. Add poppy seed, a little at a time when ice cream is almost done churning.