These lemon bars are less sturdy and more lusciously creamy than their classic bake-sale cousins. You may want to eat them with a fork.
Preheat oven to 350°. Line an 8x8x2-inch baking pan with parchment paper, allowing ends to extend over edges of pan; set aside.
In a medium bowl, beat the 1/3 cup softened butter with an electric mixer on medium speed for 30 seconds. Add powdered sugar and 3 tablespoons of the granulated sugar, the vanilla and almond extract; beat until combined. Beat in 1 egg yolk. Beat in flour and 1/4 teaspoon of the sea salt on low speed until crumbly. Bring dough together with hands, then pat evenly into bottom of the prepared pan. Bake until edges are golden and crust is set, 18 to 20 minutes.
Meanwhile, in a medium saucepan, whisk together the 2 whole eggs, the lemon zest, lemon juice, orange juice, the remaining 7 egg yolks, the remaining 1 cup granulated sugar, and the remaining 1/8 teaspoon sea salt. Cook and stir over medium heat until mixture just thickens, about 10 minutes. Remove from heat. Pour the warm lemon curd through a fine sieve into a bowl; discard solids. Whisk in the 1/4 cup cubed butter, a few cubes at a time, until melted. Whisk in cream. Pour over crust. Bake until just set with a jiggle toward the center, about 25 minutes. Remove to a wire rack to cool completely. Chill at least 2 hours. Lightly sift with powdered sugar, then cut into squares. Store leftovers in an airtight container in the refrigerator for up to 3 days.