2 cups solid vegetable shortening, or 1 cup each unsalted butter (2 sticks) and shortening
1/4 cup finely chopped mixed herbs, such as chives, dill, and thyme
1 1/4 cups buttermilk
1/4 cup heavy cream
Preheat oven to 400 degrees. In a large bowl, whisk together 4 cups flour, baking powder, baking soda, sugar, and salt. Using a pastry cutter, cut shortening into dry ingredients until texture resembles rolled oats. Add herbs and remaining 2 cups flour; gently toss to combine. Cover with plastic wrap, and chill in refrigerator for at least 20 minutes.
Make a well in center of chilled mixture. Pour in buttermilk, and stir in quickly with your hands or a large spoon until just combined. It does not matter if there are bits of unincorporated flour left in the bowl.
Turn mixture out onto a lightly floured work surface, and divide in two. Shape dough lightly into rough rectangles. Place one piece on top of the other. Transfer right onto a nonstick baking mat-lined baking sheet, preferably without sides. Roll dough out quickly and gently, being careful to not overwork dough. Pat edges to make them straight. Cut into 2-inch square pieces.
Brush tops with heavy cream. Bake until golden, 20 to 25 minutes; cover with parchment paper-lined foil if browning too quickly. Place sheets on wire racks to cool.