In a small saucepan add the strawberries, sugar, and water. Heat the mixture on medium high and mash well.
Heat until the strawberries are broken down and the liquid looks as though it has thickened a little. Strain through a fine mesh strainer and chill. I recommend putting in the freezer for faster chilling.
In a cocktail shaker, add the strawberry syrup, lime slices, and mint leaves. Muddle well, then add the rum, plus a few ice cubes. Shake well to combine.
Strain the mixture into your ice-filled glasses, then top with champagne.
Garnish with a fresh strawberry and mint, if desired.