Over medium heat, combine 1 c whole milk*, 1/2 strong coffee, 1 c sugar, 1 small pinch salt and 1 vanilla bean**. Heat gently, stirring to dissolve sugar (mixture should steam but never boil). Meanwhile, separate 4 eggs, putting the yolks in a medium bowl (whites can be frozen). Stabilize bowl with a moist towel, hold a whisk in preferred hand, and whisk eggs while slowly pouring in about 1/3 c hot milk mixture. Whisk briskly about ten seconds. Repeat with another 1/3 c. Slowly add egg mixture back to the pan, stirring, scraping the bowl clean; cook custard mixture, stirring, over medium-low heat, until thickened, 5-10 minutes. Remove from heat, stir in 1 c extra milk and 3 tbsp extra butter. Pour into a clean bowl and chill thoroughly in the fridge. Remove vanilla bean, pour into popsicle moulds or churn in an ice cream maker.
* if using lower-fat milk add slightly more butter at the end.
** if you have only vanilla extract, stir in 2-3 tsp after removing from heat.
