Place the frozen strawberries in a sieve over bowl to thaw and collect the juice. Once they are thawed, slice them and reserve 2 tablespoons of the juice. ( For fresh strawberries rinse and dry them. Cut off the leafy tops and slice in half.)
Place the sliced berries with juice in a medium saucepan over medium heat. ( Fresh strawberries will release juice as they cook). Sprinkle with sugar and mix. Allow the berries to cook until they soften about 5 minutes ( longer if using fresh berries)
Dissolve the cornstarch in the juice (or water if using fresh berries) and add to the simmering strawberries. Stir and continue to cook until it thickens about 1 to 2 minutes. Stir constantly to prevent the compote from burning. Remove from heat and place the sauce pot in ice water, taking care that water doesn't get into the pan, stir until it cools.
Add the strawberry liqueur and put the sauce in the fridge to keep cold.
Fit your electric mixer with the whisk attachment. In a medium size bowl whisk the sweetened condensed milk and strawberry compote until mixed. Keep cold.
In your chilled bowl add the cold heavy whipping cream and beat on medium-high until stiff peaks form when the whisk is lifted. Do not overheat or you'll get butter.
With a silicone spatula fold in the strawberry mixture to the whipped cream. Mix together until well mixed.
Pour into your freezer containers and cover tightly with plastic wrap. Freeze for at least 6 hours or overnight. Store in Freezer.
When ready to serve, take out of freezer for about 15 minutes. It does freeze hard but it is delicious.