To prepare the biscuit crumble, combine the flour, sugar, baking soda, and salt in a mixing bowl. Stir to combine. Add the cold sliced butter and mix the butter in until you get hazelnut size pieces of butter cut into the flour. Add the cold milk and mix just until it comes together like a crumble. Cover and set aside in the refrigerator.

Place the russet potato in a saucepan of cold water. Place over medium high heat and bring to a boil, Boil until it is cooked through or a knife is easily inserted. Drain and set aside to cool. Once it's cool enough to handle, dice into medium cubes.

Place a cast iron pan over medium heat, add the oil and butter. Once hot, add the onions and cook until soft. Add the garlic and cook for one minute. Add the potatoes and cook until crispy and golden brown. Pour the mixture into a small lightly greased baking dish.

Preheat the oven to 375F. Whisk the eggs and 1/3 cup of cheddar cheese until combined. Pour the egg mixture into the baking dish along with the potatoes. Crumble the biscuit on top. Top with grated cheddar cheese and bake just until the egg sets, approximately 15 minutes. Serve immediately.