Make a Slurry: In a mason jar with lid, shake together ¼ cup of your fresh raw milk with the cornstarch until smooth. This little trick prevents lumps - trust me on this one! Set it aside.
Heat the Milk: In a medium saucepan, whisk together the remaining milk, that pinch of salt, and sugar. Heat over medium heat until it's steaming nicely - you'll see little wisps rising from the surface. Don't let it boil though, or you'll have a mess on your hands!
Temper Those Eggs: While the milk is heating, whisk your egg yolks in a separate bowl. Once that milk is steaming, here's the important part - slowly stream about ½ cup of the hot milk into those egg yolks, whisking like crazy the whole time. This keeps the eggs from scrambling. Then slowly add the egg mixture back to the pot, followed by your cornstarch slurry. Keep cooking over medium heat, whisking constantly, until it starts to simmer and thickens up beautifully.
Finish with Love: Remove from heat and whisk in that gorgeous fresh butter and vanilla extract. The butter will make it extra silky!
Prevent the Skin: Pour the custard into a bowl and press plastic wrap directly onto the surface - this prevents that annoying skin from forming. You can serve it warm if you're impatient like my kids, or chill it for several hours for the perfect consistency.