Preheat the grill: Heat to medium-high (375–450°F / 190–230°C) and lightly oil the grates.
Make the glaze: In a small bowl, whisk together the bourbon, honey, vanilla sugar, melted butter, and salt until smooth and the sugar dissolves.
Grill the peaches: Place peach halves cut-side down. Grill for 3–4 minutes until grill marks form. Flip, then brush generously with the glaze. Grill another 2–3 minutes until tender and caramelized. Brush with any glaze again.
Transfer peaches to plates, drizzle with any leftover glaze if there is left, and sprinkle generously with granola. Serve warm.