In a mediums saucepan, combine first four ingredients. Cook and stir over medium until thickened and bubbly. Remove from heat. Set aside to cool.
Preheat oven to 325º F; position rack in lower third of oven. Grease and lightly flour a 9” x 13” baking pan.
In the bowl of a stand mixer (I use a Kitchen Aid), beat the 1 ¾ cups butter on medium - high speed for 30 seconds. Beat in the remaining 1 ½ cups sugar, scraping sides of bowl. Beat in eggs and vanilla.
Set mixer to low and begin mixing in the flour until it is all thoroughly combined.
Pour evenly into prepared pan. Spoon fruit mixture on top of batter and swirl gently to create a marbling effect, but be careful not to over mix.
Bake for 35 - 40 minutes or until edges are lightly browned and set (center may still appear a little jiggly and undone). Remove from oven and allow to cool in pan on a wire rack.