Bring cream and milk to a simmer in a heavy saucepan over medium heat. Add vanilla and 4 ounces pecans, turn off heat, cover, and let steep for 1 to 2 hours.

Whisk egg yolks and granulated sugar together in a mixing bowl until thoroughly combined. Pour dairy through a fine mesh strainer into yolk mixture, whisking constantly. Whisk to combine and return mixture to saucepan. Discard pecans and vanilla bean. Cook dairy mixture over medium heat, whisking frequently, until a custard forms on the back of a spoon but a swiped finger leaves a clean line. Strain custard into an airtight container (preferably wide and shallow), stir in ½ teaspoon salt, and chill overnight or at least 6 hours.

Churn in ice cream maker according to manufacturer's instructions. Chill in freezer until firm but not totally solid, 2 to 3 hours.

In a small, heavy saucepan, combine corn syrup, brown sugar, molasses, butter, and remaining ¾ teaspoon salt. Cook on low heat until all ingredients are combined and sugar is fully dissolved.

Stir in remaining 4 ounces toasted pecans. Stir in bourbon and reduce heat to very low, keeping sauce just warm enough to stay mobile.

Using a large spoon or flexible spatula, quickly fold pecan swirl into ice cream, just enough to distribute without integrating swirl into base. Return to freezer to harden for 2 to 3 hours before serving. Pecan chunks may have settled to the bottom of the container, so scoop all the way to the bottom when serving.