Make the cinnamon sugar: Toss the cinnamon and ½ cup (100g) of the sugar in a small bowl until the mixture is uniform. Set aside.

Preheat the oven and toast the almonds: Arrange an oven rack in the center position and preheat the oven to 300 degrees. Place the almonds on a small rimmed baking sheet and toss with 1 tablespoon of the oil to coat. Bake until the almonds are deep golden brown and fragrant, shaking half way through, 8 to 10 minutes. Remove from the oven and let cool, then toss with 1 tablespoon of the flour to coat. (Turn off the oven.)

Mix the dry ingredients: In a medium bowl, whisk together the baking powder, salt, and remaining 4 cups flour (520g) to combine.

Mix the cookie dough: In a stand mixer fitted with the paddle attachment, mix the eggs, remaining 1 cup sugar (200g) and remaining 1 cup oil on a medium high speed until smooth and homogenous, about 1 minute. Reduce the speed to low and add the vanilla and cooled toasted almonds, followed by the flour mixture. Continue to mix on low speed just until you have a smooth dough, about 45 seconds.

Chill the dough: Use a flexible spatula to scrape any dough from the paddle back into the bowl, then fold the dough several times to ensure it’s well mixed. Refrigerate the bowl uncovered for 4 hours. (My mom says it has to be exactly 4 hours but an hour less or more is fine.)

Preheat oven: Arrange an oven rack in the center position and preheat the oven to 350 degrees. 

Form the dough into loaves: Remove the chilled dough from the refrigerator and divide it into 3 equal portions (if you have a scale, each portion should be about 1 lb / 454g). Space out the 3 mounds of dough in an unlined, ungreased baking sheet. Pat each portion of dough into a smooth loaf measuring about 8x3 inches and 1 ½ inches tall. The exact dimensions aren’t important, but the loaves should all be about the same size. The dough will spread in the oven, so make sure you space them several inches apart.

Scor and sugar the loaves: USe a serrated knife to make ½-inch-deep score marks crosswise along each loaf at ¾-inch intervals. (These marks completely disappear when you bake the loaves but, according to Aunt Rose and my mom, they help you slice the cookies more easily after baking.) Using one-third of the cinnamon sugar, sprinkle it over the tops of all the loaves. 

Bake the loaves: Transfer the baking sheet to the oven and bake until the loaves are set  and the tops are golden brown, about 30 minutes. Remove from the oven and, using a fish spatula, very carefully turn each loaf over so the sugared side is down. The loaves are only partially baked and fragile at this point - try to be gentle so they don’t break. Sprinkle half of the remaining cinnamon sugar over the loaves and return to the oven. Bake for another 15 minutes, then remove from the oven and turn the loaves again. Sprinkle with the remaining cinnamon sugar and bake for a final 15 minutes. Remove the pan from the oven. Let the loaves cool slightly on the baking sheet, 10 to 15 minutes.

Slice the cookies: When the loaves are cool enough to handle but still very warm, slide the metal spatula beneath the loaves and transfer them, one at a time, to a cutting board. Use a serrated knife in a sawing motion to slice the loaves into ¾ inch thick cookies. The score marks will have disappeared during baking, so you are making fresh cuts. Let the cookies cool completely.