Prepare the crust: In a bowl, mix flour, powdered sugar, and salt. Cut in chilled butter until mixture resembles coarse crumbs. Press into a tart pan and chill for 30 minutes.

Preheat the oven to 350°F (175°C). Bake the crust for 15-20 minutes until golden. Allow it to cool completely.

In a saucepan over medium heat, combine heavy cream, chopped white chocolate, and vanilla. Stir until the mixture is smooth and creamy, then remove from heat.

Add lemon juice to the cooled mixture and stir well. Fold in the cranberries gently.

Pour the filling into the cooled tart crust and smooth the top. Chill the tart in the refrigerator for at least 4 hours, or until set.

Once set, garnish with additional cranberries and white chocolate shavings before slicing.