1/2 cup heavy cream
1/2 vanilla bean, split lengthwise and seeds scraped, or 1 teaspoon vanilla extract
1/4 cup granulated sugar
Pinch kosher salt
8 tablespoons (1 stick) unsalted butter, cubed and at room temperature
Warm the cream, vanilla bean seeds or extract, sugar, and salt in a small saucepan over medium-low heat; do not boil.
Whisk in the butter, a cube at a time, until completely melted. Pour into a serving dish and let cool to thicken slightly.