Heat your oven to 350°F (176°C). Butter and flour a 9”x 9”(23cm x 23cm) baking pan. 

In the bowl of a food processor, combine the butter, sugar and flour. Pulse until well combined, about 1 minute. Add the nuts, and pulse briefly until the nuts are just chopped. 

Pour the mixture into the prepared baking pan. Using your hands, press the mixture to form the crust. Make sure the crust is even throughout the pan. Place in the heated oven and bake for 15-20 minutes until the crust is lightly golden. 

Remove the crust from the oven but leave the oven on. Allow the crust to cool for 20 minutes. 

In a separate large bowl, whip together the eggs and sugar with a wire whisk until the mixture is lemon colored, about a minute. Add the flour, and whip until just combined, about 30 seconds. Whisk in the lemon zest and lemon juice, about 30 seconds, and then pour into the prepared crust. Place the pan in the heated oven and bake for 25-30 minutes, until the center of the lemon bars no longer seems liquid. Remove from the oven and allow to cool completely.

Sift powdered sugar over the lemon bars and cut into portions.