Preheat the oven to 300 degrees F (150 degrees C). Grease a 12-inch tart pan.
Beat butter and confectioners' sugar together in a bowl using an electric mixer until light and fluffy. Mix in flour until mixture is crumbly. Press into the prepared tart pan.
Bake crust until lightly browned, 25 to 30 minutes. Let cool completely.
Beat melted and cooled white chocolate and heavy cream in a bowl until smooth. Mix in cream cheese until thoroughly combined. Spread over cooled crust. Chill in the refrigerator for 30 minutes.
Combine 1/2 cup water and white sugar in a saucepan and bring to a boil. Mix remaining 1/2 cup water and cornstarch together in a bowl until cornstarch dissolves; add to sugar mixture. Cook and stir until mixture thickens and clears, about 5 minutes. Stir in corn syrup and return to a boil. Remove glaze from heat and let cool for 10 minutes.
Arrange strawberries, blueberries, and raspberries over cream cheese layer and brush with glaze. Chill for at least 1 hour; store in refrigerator until ready to serve.
