In a saucepan, heat the heavy cream and 1 cup sugar over medium heat, stirring, until it simmers, about 10 minutes. Meanwhile, whisk the egg yolks in a large bowl until frothy, 1 to 2 minutes. Pour the cream mixture into the yolks, whisking constantly, then pour into the saucepan. Cook over medium heat, stirring constantly with a wooden spoon, until the mixture thickens, 3 to 5 minutes.
Strain the cream mixture through a fine sieve into a stainless steel bowl, then stir in the bourbon and vanilla. Cover and refrigerate until completely chilled, about 1 hour.
Preheat a grill to medium. Brush the nectarines with the oil and sprinkle with the remaining 1 teaspoon sugar. Grill cut side down until caramelized and just softened, about 5 minutes. Let cool, then finely chop.
Pour the chilled cream mixture into an ice cream maker and freeze according to the manufacturers instructions. Add the nectarines during the last 5 minutes of freezing. Top with the pecans.