Whisk
together milk, instant coffee granules, sugar, and salt in a large bowl
until sugar is dissolved. Stir in the heavy cream, then cover and
refrigerate until chilled, at least 2 hours.
Pour the
chilled mixture into an ice cream maker and freeze according to
manufacturer's directions until it reaches "soft-serve" consistency.
Transfer half of the ice cream to a one- or two-quart lidded plastic
container. Pour half of the caramel sauce over the top, then repeat the
layers with the remaining ice cream and caramel. Swirl the caramel into
the ice cream using a chopstick or knife. Cover surface with plastic
wrap and seal. For best results, ice cream should ripen in the freezer
for at least 2 hours or overnight.