Preheat the oven to 450 degrees . Sift the first 5 ingredients into a large bowl. Using your fingers, blend in the lard until the biggest pieces are no larger than a pea. Form a well in the center of the flour mixture and add the buttermilk. Stir gently with a fork until almost blended.
Transfer the mixture to a floured work surface and knead a few times, just until the dough comes together. Pat into a large rectangle. Fold into thirds like a letter, creating 3 layers. Repeat patting out and folding 2 more times. Roll out into a 12-by-18-inch rectangle, 1/2 inch thick. Trim the edges; cut into thirty 2 1/2-by-1 3/4-inch rectangles.
Line a rimmed baking sheet with foil, shiny side up. Brush with some of the melted butter. Transfer the biscuits to the baking sheet, spacing about 1/8 inch apart. Press any dough scraps between the rim of the baking sheet and the biscuits. Brush the biscuits with the remaining melted butter; sprinkle with the flaky salt. Bake until puffed and golden, about 15 minutes.