Preheat the oven to 450°F. Spray a 9-by-13-inch baking dish with pan spray (use a smaller pan if you want to cook some biscuits now and freeze the rest for later).
In a large bowl, combine the self-rising flour, sugar and salt. Using a pastry blender, two knives, or a whisk, cut the cold butter into the dry ingredients until the butter is the size of peas LOVE NOTEDebbie prefers self-rising flour (she’s from the south, after all). If you can’t find it, you can make your own by combining 2 tablespoons baking powder and 2 teaspoons salt for every 4 cups all-purpose flour. Alternatively, you can combine the dry ingredients in the bowl of a standing mixer. Add the butter pieces, and mix first on slow, then on medium-low speed until pieces are the size of peas, about 1minute. Combine the buttermilk and heavy cream in a measuring cup. Pour it into the butter-flour mixture and stir with a wooden spoon until mostly incorporated. Then, using your hands, mix just until incorporated -- no more than 3 or 4 little kneadings. Or briefly mix on low speed with the mixer, turning it on for a couple seconds then off to scrape the sides of the bowl. Repeat until just combined. (Don’t over mix, and don’t worry that the batter is wet, goopy and non-uniform. It is okay to have some pockets of flour and chunks of butter. That’s what will make the biscuits flaky and moist. The most important thing is not to overmix!)LOVE NOTEDon’t worry if you see clumps of butter – that’s good! The little bits of butter here and there melt during cooking and yield a flaky, tender biscuit.
Put the 1 1/2 cups all-purpose flour in another shallow bowl. Using an ice cream scoop with a 1/3cup capacity or a 1/3 cup measuring cup, scoop out a heaping portion of the batter and drop it into the flour. Sprinkle some of flour on top, pick up the dough and cup it in the palm of your hand. Gently jiggle the dough in your palm so the excess flour falls away leaving just a light coating (or lightly toss the dough between both hands).
Starting in the corner, arrange the biscuits in a row down the long side of the pan so you have a row of six (you must start the first one very close to the corner and the next one nearly on top of the first in order for all six biscuits to fit. After filling the row,place two biscuits across the short side (you should now have 3 across and 6 down). Continue scooping and arranging the remaining dough directly next to each other (they should be touching and just slightly squished) in rows until you have used all the dough. (If you used a different sized baking pan, or aren’t cooking all the biscuits at once, your baking pan may not be filled corner to corner with biscuits. In this case, crumple a piece of foil to fit into the blank spaces to help the biscuits keep their shape during baking.)
Bake for 10 minutes or until biscuits start to brown, then reduce the heat to 375°F and bake until the biscuits are light brown all over, being sure to rotate the pans now and then (so they bake evenly). That should take another 20 to 25 minutes. You’ll know when they’re done when the biscuits start to pull away from each other, they don’t have any bounce when poked, and a knife inserted between some of the biscuits in the middle of the pan comes out clean.
Remove from oven, brush the tops with the melted butter, and let cool for 10 minutes before cutting into individual biscuits and serving (you could pull them apart, but I like to cut the biscuits along the obvious separations to make them a little straighter and prettier.