Instructions

for the tart

Whisk flour and salt together in bowl; set aside. Using stand mixer fitted with paddle, beat butter and sugar on medium-high speed until pale and fluffy, about 3 minutes. Add egg and vanilla and beat until combined. Reduce speed to low, add flour mixture, and beat until just combined, scraping down bowl as needed. Press dough with spatula until dough sticks together in cohesive mass. Form dough into 5-inch disk, wrap in plastic wrap, and refrigerate for at least 2 hours or up to 2 days. Let chilled dough sit on counter to soften slightly, about 10 minutes, before rolling. (Wrapped dough can be frozen for up to 1 month. If frozen, let dough thaw completely in refrigerator.)

for the curd

Cook cranberries, granulated sugar, orange zest and juice, and salt in medium saucepan over medium-low heat until cranberries have softened, 5 to 8 minutes. Mash with potato masher until cranberries are completely broken down, then strain through fine-mesh strainer into bowl, pressing on solids with rubber spatula to extract as much puree as possible (you should have about ⅓ cup). Discard solids and refrigerate cranberry puree until cooled, about 10 minutes. Wipe saucepan clean with paper towels.
 Return cooled cranberry puree to clean saucepan and whisk in egg and yolk. Cook over medium-low heat, stirring constantly with rubber spatula, until mixture is thickened and registers 170 degrees, 3 to 5 minutes. Off heat, whisk in butter until smooth. Transfer curd to clean bowl, press plastic directly on surface of curd, and refrigerate for at least 1½ hours. (Curd can be refrigerated for up to 3 days.) Adjust oven rack to middle position and heat oven to 300 degrees.
 Spray 9-inch tart pan with removable bottom with vegetable oil spray. Roll dough between 2 large sheets of plastic into 9-inch circle. Remove top sheet of plastic and gently flip dough into prepared tart pan. Press dough into even layer in pan to edge of pan, discarding remaining plastic. (Do not push dough up sides of tart pan.) Bake on rimmed baking sheet until puffed and golden, 50 to 55 minutes, rotating sheet halfway through baking. Let tart cool completely on sheet on wire rack, about 1 hour.
 Remove outer metal ring of tart pan, slide thin metal spatula between tart and tart pan bottom, and carefully slide tart onto serving platter or cutting board. Spread cranberry curd over top of tart, leaving ½-inch border around edge. Arrange blackberries and blueberries decoratively over top, sprinkle with mint, and dust with confectioners' sugar. Serve.