How to Make It
In a small saucepan, combine the cream and butter and bring just to a simmer over moderate heat.
In a medium saucepan, mix the sugar, corn syrup and water and cook over moderately high heat, without stirring, until the sugar is dissolved. Using a wet pastry brush, wash down any crystals from the side of the pan. Continue to cook, gently swirling the pan occasionally, until an amber caramel forms, about 5 minutes.
Remove the pan from the heat and whisk in the cream mixture; it will bubble up. When the bubbles subside, very carefully pour the hot caramel into a heatproof blender. With the blender on medium speed, gradually add spoonfuls of the miso until incorporated. Transfer to a bowl and let cool, then whisk in the vanilla.
Use the miso caramel as a luxurious topping for brioche French toast or mix with soy milk for a milkshake.