These wonderful bars are sweet and tangy, with a cookie base and a lemon glaze topping. They will keep for at least a week in the fridge and even longer in the freezer. Feel free to double the recipe and make them on a standard baking sheet instead of a 9x13-inch pan.
Preheat oven to 300 degrees F. Line an 9 X 13-inch baking pan with parchment paper draping over two sides.
Put the crust ingredients into a large bowl and stir with a fork until combined. Dump into the prepared baking pan and press firmly and evenly along the bottom. Bake until it begins to turn golden brown, 10 minutes.
Cool for at least 12 minutes before adding the topping. Turn oven up to 350 F.
Crack the eggs into the large bowl you used for the crust and whisk well. Add the brown sugar, flour, vanilla, and salt and whisk until smooth. Add the walnuts and coconut and stir to combine.
Pour the batter over the par-baked crust and spread with a rubber spatula. Bake until lightly brown across the surface, 20 to 25 minutes.
Make the glaze by whisking together the lemon juice, and confectioners' sugar. Add the butter and whisk until smooth. While the bars are still warm (but not piping hot), use a rubber spatula to spread the glaze over the surface. It will just coat the bars. Scatter the finely chopped walnuts over the top and shower with the zest of the 1/2 lemon.