Easy Peanut Butter Swirl Chocolate Fudge

1 cup semi-sweet chocolate chips
1 cup milk chocolate chips
1/4 cup peanut butter chips
1 (14 ounce) can Sweetened Condensed Milk, divided
2 Tbsp + 1 tsp unsalted butter, softened
pinch of salt
1 tsp + 1 dash vanilla extract