Cut the butter into cubes. The key here is to slice the butter into little 1/4" cubes. Place the chopped butter in a bowl and place in the freezer while you prepare the rest of the ingredients.

The dry components should be combined. Whisk together the flour, sugar, salt, baking powder, dehydrated onions, and baking soda in the bowl of a stand mixer. Combine the chives and cheddar cheese.

Incorporate the butter. Remove the frozen butter from the freezer and stir it into the dry ingredients. Mix on medium-low with the paddle attachment until the mixture resembles clumpy sand with pea-sized chunks of butter.

Incorporate the wet components. Stream in the buttermilk while the mixer is running, and mix just until the dough clumps together. Transfer the dough to a lightly floured work surface and shape it into an 811 rectangle.

The dough should be laminated. Fold the rectangle in thirds and press to create a 1-inch thick rectangle. Repeat folding and pressing three times more. Form the dough into a 9-inch square that's about 1" thick.

Preheat the oven to 450 degrees Fahrenheit.

Bake and cut. Cut the biscuits into 9 equal squares with a sharp knife and place on a parchment-lined baking sheet for 30 minutes. Brush with the remaining buttermilk and season with flaky salt. 18-20 minutes, or until puffy and golden brown.