While you wait for the grill to heat, toast the chopped pecans in a dry skillet over medium heat for 3-4 minutes, stirring frequently until fragrant and lightly golden. Set aside on a plate. Halve and pit your peaches, keeping them slightly firm—they should hold their shape on the grill. Have all your ingredients measured and ready: butter, bourbon, brown sugar, vanilla, and sea salt.
Melt the butter in a small saucepan over medium heat, then let it continue cooking for 3-4 minutes until it turns golden brown and smells nutty—this browning adds incredible depth to your sauce. Remove from heat immediately and carefully pour in the bourbon (it may bubble slightly). Stir in the brown sugar until fully dissolved, then return to medium-high heat and bring to a gentle boil. Let it bubble for 4-5 minutes to reduce slightly and allow the bourbon's harsh alcohol notes to cook off. Remove from heat, stir in the vanilla extract and pinch of flaky sea salt, then set aside to cool slightly. I find that letting the sauce cool for a minute or two makes it thick enough to coat the peaches without dripping off immediately on the grill.
Preheat your grill to medium-high heat (around 400°F if using a gas grill). Once hot, lightly oil the grill grates to prevent sticking. Have a pastry brush or small spoon ready for dipping the peaches into the sauce from Step 2.
Working quickly, dip the cut side of each peach half into the bourbon sauce from Step 2, letting excess sauce drip back into the bowl—you want a light to medium coating. Place the peaches cut-side down on the hot grill and cook for 2-3 minutes until you see deep caramelized grill marks. Flip carefully and grill the skin side for another 1-2 minutes just to warm through. The peaches should be tender but still hold their shape. I like to pull them off when the cut sides have that beautiful dark caramelization—it adds sweetness and complexity to each bite.
Arrange the grilled peaches on serving plates cut-side up. Drizzle with the remaining bourbon sauce from Step 2, top with a generous dollop of whipped cream, and finish with the toasted pecans from Step 1. Serve immediately while the peaches are still warm.