Caramelize the onions.
In a small pan, melt 2 tbsp of butter over medium heat and saute the onions until they turn translucent and start to brown.
Reduce the heat to medium-low and season the onions with salt, and let them cook for 15-20 minutes stirring occasionally until the onions are soft, golden brown and caramelized.
Transfer the onions to a paper-towel lined plate and let them cool completely.
Preheat the oven to 400F and line a baking sheet with parchment paper.
In a large bowl, combine flour, salt, baking powder and several cracks of black pepper and whisk to combine.
Grate the butter into the flour and use your hands or a fork to gently work the flour into the dough until just combined; do not overmix.
Add the caramelized onions, chives and cheddar cheese to the flour mixture and gently work into the butter and flour mixture until just combined and evenly distributed.
Stream in the heavy cream and use a fork to evenly distribute the liquid until a shaggy dough forms, and turn the dough out onto a lightly floured work surface.
Gently bring the dough together, and shape into a 1 inch thick square.
Using a bench scraper or sharp knife, cut the dough into four equal pieces.
Stack the pieces on top of each other and tuck in any pieces that may fall.
Gently compress the dough stack with a rolling pin and roll out the dough into a ¾ inch to 1 inch thick rectangle.
Flour the sharp end of a 3 or 4 inch round cookie cutter and punch out as many biscuits as possible, then transfer to the prepared baking sheet.
Gather and reroll the scraps and punch out more biscuits until there is no more dough.
Place the biscuit tray in the freezer for 15 minutes to firm up the butter and cheddar.
Brush the tops of the biscuits with heavy cream and optionally sprinkle with flaky salt and more cheddar.
Bake for 15-20 minutes or until the tops are golden brown.
Transfer to a wire rack and let cool for 10-15 minutes.
Serve warm and enjoy!