In a large bowl, mix together flour, sugar, salt and yeast. Add shortening and 3/4 cup buttermilk and mix with a hand mixer or in your stand mixer. Add extra 1/4-cup buttermilk, a little at a time, until dough comes together.
Knead dough by hand for 10 minutes or in the stand mixer for 8 minutes. If using a stand mixer, knead the last minute by hand. The dough should be tacky, but not sticky. Oil a medium bowl and place dough inside. Turn dough in bowl to coat in oil. Cover with plastic wrap or a kitchen towel and let dough sit until doubled in size (about 60 to 90 minutes).
Prepare a sheet pan with parchment paper and sprinkle with cornmeal. Divide dough into 6 equal pieces. Shape pieces into balls, spray with oil, and sprinkle cornmeal on both sides before placing on prepared baking sheet. Cover with plastic wrap and let the muffins rise for about an hour.
Heat a griddle to medium heat and preheat oven to 350°F. Add muffins to the griddle and cook for 5 minutes on each side. Place muffins in the oven and bake for an additional 6 minutes. Allow muffins to cool completely on a wire rack. Enjoy with butter and jam!