In a cocktail shaker combine chopped strawberries and 5 mint leaves. To muddle, gently crush berries and mint with the back of a spoon. Add cognac, lemon juice, and Simple Syrup. Add ice cubes; cover and shake until very cold. Strain liquid into an ice-filled glass. If desired, garnish with halved strawberries and a mint sprig.
In a small saucepan combine sugar and water. Bring to boiling over medium heat, stirring until sugar is dissolved. (The syrup is done when it is completely clear and the surface is covered with bubbles.) Remove from heat; cool. Store, covered, in the refrigerator up to 2 weeks.