Put flour, granulated sugar, baking powder, and salt in a large food processor and gently pulse to combine and fluff. Then, pull the buttermilk-egg mixture and unsalted butter from the fridge. Cut the butter into cubes and add it to the food processor along with the buttermilk-egg mixture. Pulse the food processor just 10-15 times to combine the ingredients. Do not overmix. Dough should be crumbly with lentil-size pieces of butter running throughout. (See TIP B for alternatives to using a food processor.)
Line a baking sheet with parchment paper or a silicone baking pad. Set the scones evenly apart on the lined baking sheet and bake in a pre-heated 375° oven for 16-20 minutes or until lightly brown on the top. You don't want the scones to over-bake so begin to watch them closely as time approaches.
TIP A: For this recipe, you just need lightly caramelized onions because they will continue to soften and sweeten in the scones as they bake. I recommend caramelizing the onion in advance and putting it in the fridge to cool so that you do not warm any of the other scone ingredients (particularly the butter). The key to perfect caramelized onions is low and slow. Set your burner to medium-low and let 1 tablespoon of olive oil come up to temperature. Cut one medium onion into thin slices and add the onion to pan in a even layer. Then just let the heat and natural sugars of the onion do their thing for about 25-30 minutes. Stir occasionally to brown all sides of the onion slices.
TIP B: My mom swears by using a food processor for this recipe because it means that she can achieve the desired crumble of the dough quickly and without using her hands (which will naturally warm the ingredients). If you don't have a food processor, you can give the ole two-knife scissor technique a try or I recommend using a multi-blade pastry blender.