Mix the half-and-half, sugar, and vanilla in a resealable bag. Push as much air as you can out of the bag before you seal it. 2. Place the ice and the kosher salt in another resealable bag. 3. Place the sealed half-and-half mixture into the bag with the ice. Now seal up that outer bag 4. Vigorously shake the bags for 5 to 10 minutes. When finished, the half-and-half mixture will harden to form ice cream.  5. Add toppings and enjoy.