In a small, non-reactive bowl toss strawberries with balsamic vinegar and sugar and set aside to macerate while you prepare the gelato.
In a metal bowl whisk together simple syrup and egg yolks, set the bowl over a pan of simmering water and whisk continuously until the mixture reaches the ribbon stage (thick, pale yellow and forms a ribbon when the whisk is lifted). Remove the bowl from the heat, transfer to the bowl of an electric mixer and beat at low speed until cool. Whisk in the mascarpone, karo syrup, milk and lemon juice and strain mixture through a fine sieve. Chill thoroughly, then process in an ice cream machine according to manufacturerís directions.
Serve with macerated strawberries.
Yield: about 1 quart