Place strawberries in a frying pan. Pour just barely enough water in to cover the bottom of the pan, then cover with a lid and turn burner onto medium.
Stirring frequently, cook until strawberries until they are completely defrosted.
Remove lid and continue to cook for about 20 minutes, until strawberries have cooked down. Add sugar.
Monitoring constantly, continue to stir until sugar has completely incorporated and sauce begins to thicken, which will occur as the water evaporates away. When mixture is the texture of bottled tomato sauce, remove from heat and turn off burner.
Allow to cool completely. This process can be sped up by stirring sauce regularly.
Carefully transfer sauce, which may be lumpy with cooked down fruit, into a blender. Blend for about 1 minute, until mixture is smooth.