Slice sweet potatoes into 1-inch cubes; place in slow cooker. In a small bowl, combine Caramelized Onion Dip Starter, brown sugar and vanilla. Pour mixture over sweet potatoes; toss to coat. Sprinkle salt over potatoes. Cover; cook on high for about 3 hours. Leave the potatoes in the slow cooker and mash. Add milk, using mixer to combine. Transfer potatoes to a casserole dish; top with french fried onions. Place in a pre-heated oven (350°) for 5-10 minutes - just long enough to heat topping. Serve immediately.