Add the strawberry reduction and condensed milk to a medium bowl and mix until smooth and set aside. For a smoother ice cream, you can reblend the mixture in a blender or food processor. (Note 3 for optional food coloring)
Add the chilled whipping cream to a bowl (if using a hand mixer), or the bowl of a stand mixer with the whisk attachment. Whip until you get stiff peaks.
Add the strawberry reduction mixture to the whipped cream. Using a spatula, gently fold the mixtures together until there are no more pink or white streaks. Try to avoid overmixing as this will beat the air out of the cream.
Scoop the ice cream mixture into a 9" (23cm) loaf pan, or airtight container. If you made the strawberry sauce, dollop it throughout the ice cream and lightly swirl the mixtures together with a knife. For example, you can dollop 1/3 of the ice cream mixture into the pan, swirl through a few spoons of the strawberry sauce, then repeat with the remaining ice cream and sauce (note 4).
Cover the ice cream and freeze for 4 hours (for a soft-serve consistency) or overnight (for a firmer consistency). Usually, you can scoop the ice cream straight from the freezer. However, if your ice cream is firmer, thaw it at room temperature for 5 minutes before serving.
Store leftover ice cream in the freezer for up to 3 weeks.