In a saucepan, add everything except the oats. Turn the heat to medium and bring it to a roiling boil. Let it boil for 1 minute, stirring occassionally, and keeping the heat at just the right level (you don't want it to burn) and then remove from the heat.
1/3 cup (75 grams) unsalted butter, 1/4 cup (60 ml) milk, 1 teaspoon vanilla extract, 3/4 cup (150 grams) granulated sugar, 3 tbsp (27 grams) Dutch-process cocoa powder, 1/4 teaspoon salt