Place a large clean glass or metal bowl into your freezer. Wash your peaches, then set a pot of water to boil. Fill your sink or a bowl with cold water and ice. Carefully slice an 'X' into the bottoms of all the peaches, through the skin, but getting as little flesh as you can.
When the pot is boiling, drop one to three peaches into the water at a time, and simmer them for about a minute. Then remove them from the boiling water and place them directly into the ice water bath.
Peel the peaches and slice in half, discarding the pit.
Preheat your grill to high. Melt the butter. Brush the peaches with the melted butter and grill until they have some great grill marks and are starting to get soft.
Slice a third of the peaches into bite sized chunks, and blend the remaining peaches into a purée.
Remove the bowl from the freezer and measure your whipping cream into it. Using a hand mixer, whip the cream until stiff peaks form.
Add in the condensed milk, vanilla, peach purée, and peach chunks, folding them into the whipped cream gently.
Line a 9 x 13 inch pan with plastic wrap (optional) and pour the whipped cream - peach mixture into the pan. Freeze for at least 2 hours or until set.
You can serve this with whatever you want, but I recommend more hot, freshly grilled peaches.