Preheat the oven to 325°F(165°C). Line baking sheet with parchment paper.
Put the flour, baking powder and salt if using in a medium bowl and stir. Set aside.
Mix the sugar and lemon zest in a medium bowl with a whisk.
Add the eggs and stir with a whisk until combined for almost 20 seconds.
Mix in the butter and lemon juice.
Add the flour mixture in 3 batches and stir with a whisk. If you are using almonds, you don't need to mix the flour mixture completely, there can be some flour visible. As you fold the almonds, all will combine. First, you can use a whisk but then you should continue with a spoon/spatula to combine.
Divide the dough in half (each dough is 365 grams)and make 8.6 inch (22 cm) long, 3.15 inch (8) cm wide logs out of each. If you find the dough sticky, don't add extra flour but flour your hands while giving shape.
Bake for 30 minutes or until the top starts to become lightly golden brown. (It becomes slightly brown at 24 minutes in my oven. I keep baking for extra 6 more minutes.)
Remove the baking sheet from the oven but don’t turn off the oven. Let them cool for almost 10 minutes before cutting each log into 0.6 inch (1.5 cm) slices at an angle. Cut the slices very gently as they are soft and crumbly.
Place each slice cut side down onto the baking sheet and bake for 20 minutes, flipping them over halfway during baking. If you want the center very soft, bake for 14 minutes or 26 minutes for a very crunchy center Let them cool completely before serving.