1. Beat egg yolks and 6 tbsp. sugar in electric mixer fitted with whisk for 1 minute at high speed.
Scrape sides and beat for one more minute until you see a steady stream or “ribbon” when you lift the whisk.
Add vanilla extract. Mix on high speed for 30 seconds.
Combine milk and 6 tbsp. sugar in small saucepan and bring to a boil over medium heat, whisking continually. Remove from heat and let cool for one minute.
Place guard on mixer and pour the milk mixture into egg mixture with mixer running on medium high speed. Once combined, pour mixture back into saucepan.
Clean mixing bowl.
Bring milk mixture to boil over medium heat, whisking continually.
Remove saucepan from heat, carefully pour into mixing bowl, and beat on high speed until cool, about five minutes.
Switch whisk to paddle attachment.
Place Greek yogurt, peanut butter, and salt in mixing bowl. Mix on medium speed until combined.
Place in freezer for 2-3 hours until solid.
Decorate with topping if desired.