Prep. Gather ingredients and prepare a 9x13" pan with a parchment paper lining. Butter the inside. Set aside.
Combine white chocolate mixture. In a mixing bowl (works best in a kitchen aid), combine (1 cube) 1/2 cup butter, 30 ounces white chocolate chips, 7 ounces marshmallow cream and 2 teaspoons vanilla. Set aside.
Melt sugar. Combine 4 1/2 cups sugar, 12 ounces evaporated milk and (1 cube) 1/2 cup butter in a large saucepan. Bring to a boil over medium heat and boil for 10 minutes, stirring occasionally so it doesn't burn. Turn down the heat if needed.
Melt chocolate. Pour hot syrup over the chocolate chips in the mixing bowl. Whip with your mixer until everything is fully incorporated.
Add fudge to pan, sprinkles with cashews. Pour fudge into prepared pan. Sprinkle cashews over the top. Evenly spread and press into the fudge. Make sure the nuts are secure in the fudge, so they wont fall off later when you flip your pan. Let set in the fridge for a few hours.
Remove fudge from pan. Turn your pan over onto the counter. Set a hot cup of water or let some hot water run over the bottom of the pan if it isn't coming out. Make sure to hold your hand over the opening so that your fudge doesn’t drop into the sink. After a couple of seconds of hot water the fudge should release.
Slice into pieces. Drop the pan over onto parchment paper so you can cut it into pieces. Then slice into 40 squares.
Notes
Storage:Store in a covered container for 2-3 weeks. Freeze for up to 6 months.