How to Make It
In a standing electric mixer fitted with the dough hook, combine the flour, baking soda and 2 teaspoons of salt. Add the lard and mix at medium-low speed until evenly combined. Slowly add the water, mixing until the dough forms a mass around the hook. Increase the speed to medium and knead until smooth, 5 minutes. Divide the dough into 6 pieces and roll each piece into a ball. Wrap the balls in plastic and let rest at room temperature for 30 minutes.
Preheat the oven to 225°. Heat a cast-iron griddle until very hot. On an unfloured work surface, roll out each ball to a 10-inch round, about 1/8inch thick. Brush both sides of each round very lightly with oil and grill over moderate heat, turning once, until golden and cooked through, 3 to 4 minutes. Wrap in foil and keep the breads warm in the oven while you cook the rest.
In a small bowl, season the ricotta lightly with salt and pepper. In a medium bowl, toss the arugula with the 1 tablespoon of oil and the lemon juice and season with salt and pepper. Arrange 3 breads on a work surface and spread with the ricotta. Top with the prosciutto, followed by the arugula salad. Cover with the remaining breads, cut into quarters and serve warm.