Preheat the oven to 400 degrees F. Line a baking sheet with parchment paper.
In a large bowl, combine the flour, granulated sugar, baking powder, salt and baking soda and whisk well to combine. Next, add the butter and lemon zest and combine the mixture with a fork until coarse crumbles are created. Add the buttermilk and mix until just combined. Make a disk with the dough and cover in plastic wrap. Chill for 15 minutes.
Dust a cutting board with flour. Roll out the dough to about 3/4-inch thickness. Cut the biscuits with a 1 1/2-inch floured cookie cutter, juice glass or something similar. Reroll the remaining dough and continue making biscuits.
Place the biscuits on the prepared baking sheet. Brush the tops with the beaten egg and sprinkle with the raw sugar. Bake until golden brown, about 15 minutes.