In a large bowl, with a mesh strainer set on top, add 1 cup heavy cream. Set aside.
In a medium saucepan over medium heat, combine remaining heavy cream, whole milk, sugar, salt and vanilla. Stir to combine and dissolve sugar. When mixture begins to steam, slowly drizzle 1 cup hot liquid into egg yolks while whisking continuously. Transfer egg mixture to saucepan. Continue cooking until mixture coats the back of a wooden spoon or rubber spatula. Pour through mesh strainer into reserved heavy cream, discard any solids. Cool over an ice bath to room temperature.
In a blender, combine custard mixture with apple butter. Process until smooth and combined. Transfer to a large bowl. Cover and place in refrigerator until thoroughly chilled or overnight.
Preheat oven to 375°F. In a medium bowl combine crumble ingredients by hand. Break up into no larger than 1/2-inch pieces. Transfer to a 9x13 baking pan. Bake for 10 minutes. Cool completely before adding to ice cream.
Churn ice cream according to manufacturer's directions. Alternate layers of ice cream and crumble in a freezer safe container. Transfer to freezer until firm.