Place the flour, confectioners' sugar, butter and salt in a food processor. Cover and pulse until mixture resembles coarse crumbs. Add egg yolk, processing just until mixture forms a soft dough. Shape into a ball, then flatten into a disk. Wrap and refrigerate for at least 1 hour. , Press dough onto the bottom and up the sides of an ungreased 9-in. fluted tart pan with a removable bottom. Bake at 400° until golden brown, 10-12 min. Cool on a wire rack. Reduce heat to 325°., In a small heavy saucepan over medium heat, whisk the eggs, lemon juice, sugar and lemon zest until blended. Add butter; cook, whisking constantly, until mixture is thickened and coats the back of a spoon. Pour into crust. Bake for 8-10 minutes or until set. Cool on a wire rack. , Spread preserves over tart. Garnish with mint if desired. Refrigerate leftovers.