Prepare. Mix together ranch dip mix and sour cream until well combined. Cover and keep in the fridge while you prepare other ingredients.
Mix Dry Ingredients. In a large bowl whisk together flour, baking powder, and salt. Toss in butter. Cover bowl and place in the freezer for about 10 minutes until ingredients are cold.
Cut in Butter. Using your fingers, rub chilled butter into flour mixture. Work the butter into the flour to create a lumpy mixture. Work quickly to keep everything cold.
Add Wet Ingredients. Stir in the sliced scallions. Add chilled ranch sour cream mixture. Use a spatula to stir contents together until dough begins to form. It will look very dry and shaggy.
Dump mixture onto clean work surface. Use your hands to press dough together. Roll it to a rectangle about ¾-inch thick. Cover with plastic wrap and let rest in the fridge for 10 minutes.
First Lamination. Uncover chilled dough. Divide dough into thirds and stack. Press down to ¾-inch thick. Wrap and chill for in the fridge for 10 minutes.
Repeat Folding. Uncover dough. Halve and stack again. Roll to about one inch thick.
Cut Biscuits. Trim the edges of the dough with a sharp knife to expose the layers. Cut biscuits using a sharp knife or biscuit cutter, pressing straight down. Gently press scraps together for additional biscuits (note: these won't rise as dramatically). Keep cut dough in the fridge while you preheat oven.*
Arrange and Bake. Preheat oven to 400°F. Line baking sheet with parchment paper or silicone baking mat. Arrange biscuits on baking sheet, spacing them about 2-inches apart. Lightly brush tops with heavy cream. Bake for 25-28 minutes until biscuits have risen and are no longer pale.
Serve. Cool in pan for 5 minutes, then serve warm. These are best enjoyed fresh from the oven.