Sift the dry ingredients into a large bowl and cut the softened butter and the additional fat of choice (bacon grease, lard, shortening, etc) into cubes and with your clean fingertips mash the chunks with the flour until they are only about the size of small peas.

Add buttermilk, yogurt, cheese & jalapenos and mix lightly but thoroughly. The dough should be soft, but not sticky. (If the dough is too dry add a few drops of milk, if it is sticky dust with a little extra flour.) When the dough is soft but not sticky cover the dough in a mixing bowl and place in refrigerator to cool for at least 20 minutes, preferably overnight.

After dough cools in the fridge preheat the oven to 450 degrees and place cast-iron skillet in oven to begin heating. Roll the biscuit dough to about 3/4″ thick on a lightly floured surface and use biscuit cutter (or drinking glass if you want larger biscuits) to cut out the dough.

Bring the hot cast-iron skillet from the oven and place cut biscuits in the skillet and return the skillet to the oven, baking for about 12 minutes (depending upon how thickly you cut the biscuits.)