Preheat the oven to 400ºF.
Slice the grapefruits in half lengthwise. Segment the grapefruit by using a small sharp knife to loosen the segments from the membrane. Place the grapefruits cut size up in a baking dish.
Drizzle each grapefruit half with honey, olive oil, vanilla extract, and a pinch of salt.
Roast the grapefruit for 15-20 minutes until the grapefruit is warmed through and lightly caramelized around the edges. If desired, switch the oven to broil, and broil for 1-2 minutes at the end just for extra color. Keep an eye on this.
Using an electric mixer, beat the cream until desired consistency. Dollop on the grapefruit and finish with a sprinkle of kosher salt and the pistachios.
