Place whipping cream in a medium saucepan with ½ the sugar on medium heat. Bring to a simmer and cook stirring constantly for about 3 minutes. Turn off heat.
Combine the rest of the sugar and egg yolks and vanilla in a mixing bowl, whisking until smooth. Slowly add warm cream to egg mixture, whisking constantly. Transfer egg mixture into a double boiler over simmering water. Whisk mixture constantly about 9 minutes or until thickened and coats back of spoon. Stir in the cornstarch and vodka slurry and cook for 3 more minutes stirring constantly. Remove top from heat, and place in the refrigerator for cooling, stirring occasionally with a spatula; allow mixture to cool completely. Mixture will thicken slightly while cooling. When cooled transfer cold custard into a piping bag and keep refrigerated until ready to fill the peaches.
Cut tops off peaches, and carefully hollow them out, discarding pit using a pit remover. (Slice a thin portion from bottoms, if needed, to help peaches sit upright.) Fill each peach with about 1/4 cup custard, smoothing so mixture is even with top of peach. Refrigerate until ready to serve, at least 4 hours to set or overnight would be best.
Sprinkle a thin layer of sugar onto each custard-filled peach; caramelize sugar using a kitchen torch, keeping torch moving at all times for even coloring. Serve within 1 hour of browning sugar.