Preheat the oven to 350°F

Cut the butter into small pieces.

Measure the flour and sugar into the large mixing bowl. Stir together. Add the butter.

Cut the butter into the flour and sugar and blend until a loose ball forms. You may have to use your hands to help form the ball.

Press the dough evenly into the bottom of your 9 x 13 inch pan.

Bake, unfilled, for 16 - 18 minutes. Turn the pan about halfway into the cooking time.

While the crust is baking, wipe out the mixing bowl.

Beat the eggs and vanilla briefly with the whisk.

Add the flour and sugar. Whisk to mix.

Zest the lemons directly into the mixing bowl.

Juice the lemons and add the juice to the mixing bowl. I like to collect the juice in a small bowl and pour it through a strainer to catch the seeds. I've also collected the juice in a bowl and picked the seeds out by hand.

Use the whisk to beat the mixture until the sugar is dissolved. By the time this happens the custard should be lighter in color and you will no longer hear/feel the whisk scraping against the sugar.

When the crust is ready remove it from the oven and pour the filling over the crust. Spread the filling with a spatula or by tipping the pan if necessary. Be careful if using the jelly roll pan, it will be quite full.

Return to the oven and bake for another 20 minutes. The lemon bars are done when the filling is set.

Allow to cool for a few minutes then sprinkle with powdered sugar.

Cut into bars and serve. For a 9 x 13" pan, I get 24 pieces.