For the crust: Preheat the oven to 350 degrees F. Grease a 9 by 13-inch baking sheet (otherwise known as a quarter sheet pan) with some cooking spray.
In a stand mixer with the paddle attachment (or you can use a food processor), cream your butter with the sugar and almond extract until light and fluffy. Whisk the flour and salt in a small bowl, making sure there are no lumps. Turn the mixer speed to low, add the flour into your butter and mix until just incorporated. (Make sure not to over-mix.) Turn the dough onto the baking sheet, flour your hands and press it out evenly on the bottom and up the sides. Pop in the fridge for an hour (or overnight) to chill.
Pop the crust in the oven and bake until a light golden brown, about 20 minutes. Cool completely on a wire rack.
For the filling: While the crust is cooling, make your filling. Crack your eggs into a large bowl and add the sugar, lemon zest, lemon juice and flour. Whisk until combined. Pour into the crust and spread evenly. Put back in the oven and bake until the filling is completely set, about 30 minutes. Let cool to room temperature before serving.
Dust with confectioners' sugar and then cut into 20 to 24 squares to serve. Garnish with raspberries, if desired.