Preheat oven to 400° F and grease or line a cookie sheet.
In a large bowl, beat the egg.
1 egg
Add sour cream and sugar and whisk until fully incorporated.
1 cup sour cream, 1 tablespoon granulated sugar
Use a cheese grater to grate cold butter into the bowl. Stir just into to combine.
¼ cup butter
Add the remaining dry ingredients - flour, baking soda, baking powder, and salt. Mix just until a sticky dough forms.
2 cups all-purpose flour, ½ teaspoon baking soda, ¾ teaspoon kosher salt, 1 teaspoon baking powder
Lightly flour a clean counter surface or cutting board. Place the dough onto the floured surface.
Lightly flour your rolling pin and roll out the dough until it’s about 1 inch thick. Do not over-flour the dough.
Use the opening of a wide-mouth 16 oz mason jar, a glass, or a biscuit cutter. (If you use something that is smaller or bigger, that’s fine! It might change the number of biscuits.)
Place the biscuits on the prepared baking sheet.
Cook for about 15 minutes at 400°F until golden brown.
Remove from oven and enjoy! (Brush the tops with butter when they come out of the oven if desired.)