Combine the cream, sugar, scraped vanilla beans, vanilla pod and honey powder in a saucepan over medium heat. Bring to a simmer, stirring constantly, until all the sugar dissolves. Sprinkle the gelatin over 2 tablespoons cool water in a bowl. In a heatproof container with a spout, combine the gelatin mixture with the heated cream, allowing it to dissolve. Whisk in the buttermilk.
Add 1 tablespoon of buckwheat honey to the bottom of each of four 8-ounce parfait glasses. Divide the panna cotta evenly among the glasses, about 6 ounces in each. Refrigerate until firm, about 3 hours. Drizzle with more honey and sprinkle with the pistachios.
Honey powder is dehydrated honey. It can be purchased online or at a specialty store. If you can't find it and don't mind a darker color, use regular honey instead.