To a small bowl, add the instant yeast, warm water (temperature of baby's bathwater) and sugar. Set aside while you mix the other ingredients. The yeast will smell yeasty and become bubbly during this time.
Add the flour, baking soda, baking powder and salt to a large bowl. Stir together to combine.
Cut the shortening into the flour mixture using a pastry cutter (affiliate link), your fingers or two knives. Continue until the shortening is in very small pea-shaped pieces.
Using a box grater, grate the cold butter on the edges of the grater. Add the cold butter to the flour mixture. Mix to combine.
To the flour/butter mixture, add the reserved yeast and the buttermilk. Mix gently until the dough forms a ball.
Turn the dough out on the counter and fold over once or twice, being careful not to overwork the dough.
Pat and roll the dough into a large rectangle (roughly 20 inches by 13 inches) and 1/2 inch or more thick. Cut the dough into 20-24 rectangular pieces (depending on how many you want) using a bench knife (affiliate link) or sharp knife.
Fold each rectangle in half and place in a greased 9 by 13 baking pan. Continue filling up the pan and nestling the rolls together.
Cover with a kitchen towel and let rise about an hour. The time may vary based on the temperature of the buttermilk and the temperature of your kitchen.
Once the biscuits have risen (puffed up and approximately doubled in size), preheat the oven to 425 degrees.
Bake biscuits for 20 minutes until golden brown on top.
As soon as they come out of the oven, brush melted butter on top of the biscuits. Continue brushing until all the butter is used up. Enjoy immediately!