Prepare the tart crust: In a mixing bowl, combine flour, powdered sugar, and cubed butter. Mix until crumbly.
Add the egg yolk and mix until just combined, then press the mixture into the tart pan.
Chill the crust in the refrigerator for about 30 minutes to set.
Preheat the oven to 350°F (175°C).
Bake the crust for 15-20 minutes, until lightly golden.
While the crust bakes, prepare the filling: In a saucepan, heat the heavy cream until it simmers.
Remove from heat and stir in the white chocolate chips until melted and well combined.
Add vanilla extract, cornstarch, and mix until combined.
In a separate bowl, mix the cranberries with granulated sugar and let sit for about 10 minutes.
Pour half of the white chocolate mixture into the baked tart crust, then top with cranberries, and finish with the remaining chocolate mixture.
Bake for an additional 20-25 minutes until the filling is set and slightly puffed.
Allow the tart to cool completely before serving; chilling it in the refrigerator can enhance the flavors.