In a mixing bowl, combine heavy cream, milk, sugar, and vanilla extract. Stir until the sugar is dissolved.

Pour the ice cream mixture into a zip-top bag and seal tightly, removing as much air as possible.

In a larger zip-top bag, add ice and salt. Place the smaller bag with the ice cream mixture inside the larger bag, and seal the larger bag tightly.

Shake the bags vigorously for about 5-10 minutes until the ice cream thickens.

Remove the smaller bag from the larger bag, wipe it down to remove salt, and carefully open it. Scoop out the ice cream and serve immediately.