Add the yeast to the warm water and stir to combine. Set aside until foamy.
In a large bowl, combine 5 c. of the flour, salt, baking powder, baking soda and sugar.
Cut the cold butter and shortening into the dry ingredients until the mixture resembles small peas. Add in the lemon zest.
Add the yeast to the buttermilk and stir lightly. Pour the liquid into the dry mixture. Work the ingredients together, just until all comes together. Do not overwork.
Gently fold in the blueberries.
Sprinkle the remaining ½ c. flour onto your work surface.
Dump the dough onto the floured surface and knead the dough, just until it forms a ball.
Using your hands, press the dough into a rough rectangle. Fold dough in half and press into a rectangle again two more times. Finally, press dough out to approx. ¾ inch thickness.
Using a biscuit cutter, press cutter straight down into the dough to cut the biscuits. Do not twist the cutter. Doing so can seal the edges of the dough, keep it from rising well. I used a 3-inch cutter which produced 13 biscuits. You may use a smaller cutter, producing more, smaller. biscuits.
Place the biscuits onto a lightly greased iron skillet or parchment-lined baking sheet. Cover with a slightly damp towel and allow to rise in a warm place for about 1-hour and 15-minutes.
Preheat oven to 400-degrees.
Bake on center rack of the oven for about 12-15 minutes or until golden brown.
Remove from oven and brush tops with the melted butter.
Remove from pan and cool on wire rack.