These classic crackers are perfect for dotting over a thick soup like clam chowder.
In medium bowl, combine yeast, sugar, and water. Let stand in warm place until creamy, about 5 minutes. Using a wooden spoon, stir in 3 1/2 cups flour until well combined. Form into a ball. Transfer to a clean, oiled bowl; cover with oiled plastic wrap. Let rise in a warm place until doubled, about 2 hours.
In a small bowl, dissolve baking soda in 1 tablespoon water. Stir baking-soda mixture, buttermilk, salt, and shortening into yeast mixture; if necessary, knead to combine. Gradually stir in enough remaining 1 cup flour to create a soft but not tacky dough.
Transfer dough to a lightly floured surface; knead until firm, about 7 minutes. Cover loosely with plastic wrap; let rest for 15 minutes. Knead dough until becomes elastic and smooth, about 5 minutes. Transfer to lightly oiled bowl; cover tightly with oiled plastic wrap. Let rise in a warm place for 2 hours.
Heat oven to 325 degrees. Turn dough onto a well-floured surface; roll into a 12-by-17-inch rectangle. Fold into thirds, and roll out to original size again. Repeat folding-and-rolling process. Cut off 1/2 teaspoon of dough. Form into ball by stretching dough over itself and pinching at bottom to secure. Roll in flour, and place on ungreased baking sheet. Repeat process until all dough is used. Bake crackers for 40 minutes, until cooked through completely. Transfer to wire rack to completely cool. Store in an airtight plastic container.