Combine sweetened condensed milk, whole milk, evaporated milk, cream, sugar, molasses, and vanilla extract together using a whisk in a large bowl, taking care to avoid creating bubbly foam. Refrigerate mixture for 30 minutes.
Preheat oven to 350 degrees F (175 degrees C).
Melt butter in a large saucepan over medium-low heat; stir in salt until dissolved. Mix pecans into melted butter until evenly coated. Spread coated pecans in a single layer onto a baking sheet.
Bake in the preheated oven for 6 minutes. Flip pecans and continue baking until toasted and fragrant, about 6 minutes more. Remove butter pecans from oven and coarsely chop. Measure 1 1/2 cups butter pecans and reserve the remaining for another use.
Pour cream mixture into an ice cream maker and follow manufacturer's instructions for ice cream. When ice cream is semi-solid (about 30 minutes), stop the machine. Pour ice cream into an air-tight container and fold in 1 1/2 cup butter pecans. Cover ice cream with plastic wrap and seal container with a lid. Freeze ice cream until solid, at least 2 hours.
