Melt the margarine and lard together and set aside to cool to lukewarm.
Put the molasses in a very large and heavy smooth-bottomed pot. Stir in the cloves, cinnamon, ginger, and the brown sugar. Turn to medium-high and start stir with a wooden spoon until the mixture is warm, the sugar has dissolved, and all the spices are incorporated, 5 to 10 minutes. Do NOT bring it to a boil.
Put the salt and soda in a cup or small bowl and mix it with about 3 tablespoons flour in a cup. Add that to the molasses mixture. Stir until completely dissolved, mashing any particles of soda against the side of the pot so that every bit is incorporated.
Pour in the cooled margarine and lard, and beat with a wooden spoon until completely blended. Allow the whole mixture to cool before adding the flour, or the dough will absorb more flour. Add about one-third of the flour mixture and stir well with a wooden spoon. Add the second third of flour and continue to mix.
Take the remaining third of flour and sprinkle a work surface thickly with some of it. Scrape all the dough out onto the floured surface, and begin to knead, flouring your hands frequently while you incorporate the remaining flour.
When the dough has become stiff and firm and far less sticky, roll it into a long tube and cut it into eight pieces, which will weigh roughly one pound each. Shape each ball into a disk, slapping the surface with your hands to smooth it (you'll see the lard rise to the surface, making each disk kind of shiny).
Put four disks of dough in each of two large plastic bags and seal. Allow to sit overnight on the countertop. The dough will swell some and the spice flavors will mellow and blend.
When you're ready to bake, preheat the oven to 250 degrees F. Cover a pastry or rolling board (or a square piece of plywood) with bleached muslin that's been washed several times, tacking it tightly around the edges. Flour the muslin and rub the flour into the cloth to coat it deeply. Roll the cookies as thin as possible, 1/16 to 1/32 of an inch. Cut with any cookie cutter you like, using tiny cutters such as hearts or circles to cut out little cookies in the spaces between larger cookies. (You can also gather the scraps and reroll, but these cookies won't be as tender.)
Lift the cookies onto an ungreased baking sheet and bake for 10 minutes. Watch them, and don't let the cookies brown around the edges. Allow to cool on the pan for several minutes before lifting them onto cooling racks. As soon as they're completely cool, pack and store in an airtight container. If you're using cookie tins, seal the lid of the tin with masking tape. Any air creeping in will cause the cookies to soften.
Recipe courtesy of Evelyn Sellers, Winston-Salem, North Carolina