Preheat the oven to 375º F (180º C). Line a square cake pan or mold of about 7.8 inches (20 cm) with parchment paper.
In a food processor (not a blender) put the flour, salt and confectioners sugar. Process for 30 secodns until the ingredients integrate.
Add in the butter in cubes and process for another 30 seconds until a sand-like dough forms (this whole dough process can also be made in a bowl using your fingertips being careful not to overwork the dough.
Put the dough in the cake pan and press it to even it out using your hands until you have a base and make the edges be tall of about 0.80 inches (2 cm).
Refrigerate the dough in the cake pan for 30 minutes or freeze it for 15 minutes.
Bake the crust at 375º F (180º C) for 15 to 20 minutes until it turns slightly golden brown. Take it out of the oven and set aside until needed.
In a big bowl using a whisk, mix all the ingredients to make the filling for 1 minute until you have a smooth mixture.
Pour this over the crust and bake again all together for 30 to 35 minutes until the surface looks firm and slightly golden brown.
Take out of the oven and let it cool down completely inside the pan for about 30 minutes. Once cold, cut it into 12 to 16 squares.
Serve the bars decorating them with some confectioners sugar on top if desired.
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