In a mixing bowl, whisk together the pastry flour, baking powder, salt, and baking soda. Cut the butter and leaf lard into cubes (roughly 1 inch) and toss them in the flour mixture. Put the bowl in the freezer until the butter and leaf lard are completely frozen, about an hour.
Once the fats are frozen and the dry ingredients are icy cold, transfer the mixture to a food processor and pulse until pea-sized chunks of fat are distributed throughout the flour.
Transfer the mixture to a large bowl and add the all-purpose flour. Toss until the butter and lard are spread evenly throughout.
Add 1 1/4 cups of the buttermilk and mix gently. Test to see if the dough holds together when you squeeze it. If it doesn’t, add the remaining 1/4 cup buttermilk, tablespoon by tablespoon, until it does.
Line a baking sheet with parchment paper or a silicone baking mat. Bring the dough together on a lightly floured surface and roll to 3/4 to 1 inch thick. Cut the dough into 3-inch rounds with a circle cutter and place the biscuits on the lined baking sheet. You can re-roll once with the leftover scraps of dough, but that batch won’t be quite as flaky.
Place the biscuits in the freezer while you preheat the oven to 400° F.
Beat the egg and cream together and brush the tops of the cold biscuits with the egg wash.
Bake until golden brown, 20 to 25 minutes.
Note: These biscuits freeze really well, just egg wash them right before baking. They can go into the oven still completely frozen, just increase the baking time by about 10 to 12 minutes.
Cara Nicoletti is a butcher and writer living in Brooklyn, New York. Cara started working in restaurants when she moved to New York in 2004, and was a baker and pastry chef for several years before following in her grandfather and great-grandfathers' footsteps and becoming a butcher. She is the writer behind the literary recipe blog, Yummy-Books.com, and author of Voracious, which will be published by Little, Brown in 2015. She is currently a whole-animal butcher and sausage-making teacher at The Meat Hook in Williamsburg.