You can make your own self rising flour by combining 1 cup all-purpose flour, 1 1/2 teaspoons baking powder and 1/4 teaspoon fine salt.
1. Heat oven to 400°F. Combine flour, cold bacon fat, and salt in a bowl and mix until pea-size crumbs form; add mashed potatoes and milk, mixing to form a smooth dough. Roll out onto a lightly floured surface into a 9½" x 9½" square. Cut into twenty 2½" squares, rerolling dough as needed.
2. Bake on a parchment paper-lined baking sheet until lightly golden, 20 minutes, rotating pans halfway through; transfer to a wire rack to cool. Heat bacon fat over medium-high heat; cook bread until warmed through and golden, flipping once, about 2 minutes. Serve warm with scallions if you like.