I found a great tutorial of sorts on Joy th Baker.
1c heavy whipping cream
1/4t sea salt
Put whipping cream in your stand mixer with whisk attachment and whip... and whip... and whip until the fat separates from the milk. Use a wire mesh strainer to strain the milk out (the buttermilk) and put it bake into the mixer and beat a bit longer to solidify it. Add in the salt and voila! Butter! The boys really enjoyed watching it turn from liquid to solid and enjoyed it all the more melted onto some fresh bread!