Preheat grill to medium heat. Gently brush each peach half with oil and place it cut side down on the grates. Cook for 2-3 minutes. Use tongs to carefully rotate peaches a quarter turn and cook for another 1-2 minutes. Remove peaches from grill. Cool slightly.
In a small bowl, combine mascarpone (or cream) cheese, powdered sugar and vanilla and beat with a hand mixer on medium speed until light and fluffy. Set aside.
When ready to serve, spoon a small scoop of cheese mixture into the hollow of each peach. Drizzle peaches with balsamic glaze and sprinkle with pistachios.
Mascarpone cheese is often found in the deli section of the grocery store. Feel free to swap in regular cream cheese if you prefer.
Choose peaches that are ripe but still relatively firm. Overripe peaches will lose their shape and get mushy once heated on the grill.
You don't need to add a lot of oil to the peach halves but make sure the cut sides are brushed well with oil so the peaches don't stick to the grates. A hot, preheated grill also helps with this.
Enjoy these peaches while still warm. They may start to weep and lose shape if made too far in advance.
Slice any leftovers, refrigerate and toss in a salad.