Line a 9×9 inch baking pan with parchment paper, leaving a 3-inch overhang on all sides.

In a standing electric mixer fitted with the paddle attachment, beat Earth Balance and confectioners' sugar until fluffy. Add in flour and salt into bowl; mix on low speed until combined. Transfer dough to prepared pan and press evenly into bottom of the pan using the back of a measuring cup; it should be about 1/4 inch thick. Transfer prepared pan to refrigerator; chill until firm, about 30 minutes.

While pan is chilling, preheat oven to 325 degrees F. Transfer chilled baking pan to oven and bake until crust is golden brown, about 20 minutes. If crust appears to be browning unevenly, rotate pan.

Meanwhile, whisk together eggs or egg substitute, baking powder, and salt in a large bowl. In a separate bowl, whisk together flour and sugar. Add lemon juice and zest into the bowl of flour and sugar mixture, then whisk to dissolve granulated sugar. Add egg mixture to flour mixture and whisk until well combined and smooth.

When the crust is golden brown, pull out oven rack and evenly pour filling mixture directly over hot crust. Place pan back into oven. Reduce oven temperature to 300 degrees F and bake until center is set, about 30 to 40 minutes.

Remove baking pan from oven and transfer to a wire rack to cool. Let lemon bars cool completely before covering and transferring to refrigerator until chilled. Best results will be obtained by cooling overnight.

Sift confectioners sugar over the top of the squares, if desired, then cut into squares and serve.