Preheat oven to 350 degrees. On a baking sheet spread almonds and toast for about 5 minutes until lightly golden. Cool and grind in a food processor or finely chop

Into a medium bowl, sift together 1 1/2 cups flour, the confectioners' sugar, and the salt. Cut in the butter, 1 teaspoon zest, and almonds until mixture just clings together.

Press mixture into a lightly buttered 9-by-13-inch baking dish. Bake until just firm and lightly golden, about 20 minutes. Let cool slightly before filling.

In a large nonreactive bowl, stir together the granulated sugar, eggs, lemon juice, baking powder, and remaining 1/4 cup flour and tablespoon zest until combined. Pour into prepared crust.

Bake until filling is set and lightly browned, 25 to 30 minutes. Transfer to a wire rack to cool. Cut into squares.

If desired dust top with powdered sugar.