In a mixing bowl, combine all-purpose flour and powdered sugar. Cut in cold butter until the mixture resembles coarse crumbs. Press this mixture firmly into a tart pan. Freeze the crust for 30 minutes until firm.

Preheat your oven to 350°F (175°C). Once the crust has chilled, remove it from the freezer and bake for about 20 minutes, or until edges are lightly golden.

Whisk together eggs, lemon juice, lemon zest, and granulated sugar in a medium saucepan. Heat over medium heat, stirring constantly, for about 8-10 minutes or until thickened.

Remove the lemon curd from heat and strain through a fine sieve into a bowl to eliminate lumps. Stir in butter until fully melted and smooth.

Spread the lemon curd evenly into the cooled tart crust. Cover and place in the refrigerator to chill for at least 2 hours.

Blend fresh or thawed blueberries until smooth. Once the tart is set, pour the blueberry sauce over the lemon curd layer.

Return the tart to the refrigerator for an additional 30 minutes to allow the blueberry layer to set. Slice and garnish with fresh blueberries and powdered sugar.