Place nuts in a shallow pan and bake in a 180ºC oven for 6 to 8 minutes or until golden brown. Let cool. In a mixing bowl, cream butter and sugar until light and fluffy. Beat in eggs, lemon juice and zest. In a bowl, combine the flour, baking powder and salt. Add to the creamed mixture, mixing until blended. Fold in nuts. Divide dough in half. On a greased and floured baking sheet pat out into two logs about 1 cm high, 4 cm wide and 36 cm long, spacing them at least 5 cm apart. Bake in the middle of a 160ºC oven for 25 minutes or until lightly browned. Transfer from the baking sheet to a rack. Let cool for 5 minutes. Place on a cutting board. With a serrated knife slice diagonally at a 45 degree angle about 1 cm thick. Lay the slices flat on the baking sheet and return to the oven for 10 minutes longer, turning them over once, to dry slightly. Let cool on a rack. Store in a tightly covered container. These cookies keep well. Makes about 3.5 to 4 dozen.