Preheat the oven to 350 degrees F. Grease and flour a 9x13-inch pan.
PREPARE THE CRUST:
In a medium bowl, use an electric mixer to beat the flour, sugar, butter, eggs and chocolate syrup until smooth. Pour into the prepared pan and bake 25 to 30 minutes, or until cooked in the middle. Cool completely.
PREPARE THE MINT CREAM LAYER:
Use an electric mixer to combine the powdered sugar, butter, water, mint extract, and green food coloring. Spread evenly over the cooled cake. Chill.
PREPARE THE CHOCOLATE TOPPING:
In a medium glass bowl, microwave on high the butter and chocolate chips until melted (or heat on low in a small saucepan on the stove). Stir until smooth. Pour the chocolate topping on top of the mint layer. Spread evenly. Cover and chill. Cut into squares when firm. Keep squares refrigerated until ready to serve.