Combine cream, milk, salt and 1/4 cup of the sugar in a medium saucepan. Crush vanilla finely and stir into mixture. Bring to a simmer and stir until sugar dissolves. Remove from heat, cover, and allow to rest for 30 minutes.

Whisk together egg yolks and the remaining 1/4 cup sugar about 2 minutes or until pale. Slowly add 1/2 cup of the cream mixture from step 1, whisking constantly. Once combined, add this to the remaining cream mixture and cook over medium heat until thick enough to coat a wooden spoon, about 2-3 minutes.
Transfer to a bowl set over ice water and allow to cool, stirring intermittently.

Halve peaches and remove stones. Grill face down over an open flame until just slightly blackened, then remove. Once cooled, remove peels and chop into a small saucepan. Add the maple sugar and 1 tbsp water and cook over medium heat until syrupy, around 7-9 minutes, stirring occasionally. Remove from heat and stir in bourbon, then allow to cool.

Process custard in an ice cream maker according to manufacturer directions, then fold in peach mixture. Transfer to an airtight container and freeze until firm, about 4-6 hours.