Preheat the oven to 425°F (220°C) and line a baking sheet with parchment paper.
In a mixing bowl, combine the all-purpose flour, baking powder, garlic powder, dried parsley, salt, and black pepper. Whisk until well mixed.
Cut in the cold cubed butter using a pastry cutter or fork until the mixture resembles coarse crumbs.
Stir in the shredded cheddar cheese.
Gradually add the buttermilk to the flour mixture, stirring gently until just combined. Do not overmix.
In another bowl, combine all the crab filling ingredients (crab meat, cream cheese, mayonnaise, Dijon mustard, lemon juice, and Old Bay seasoning). Mix until well blended.
Turn the biscuit dough onto a floured surface and knead gently 3-4 times. Roll the dough to about 1-inch thickness.
Cut out circles using a biscuit cutter or glass (about 3 inches in diameter). Place half of the biscuits on the prepared baking sheet.
Take a spoonful of the crab filling and place it in the center of each biscuit on the baking sheet.
Top each with another biscuit circle and pinch the edges to seal.
Bake in the preheated oven for 15 minutes or until golden brown.
While the biscuits are baking, prepare the lemon butter by mixing melted butter, lemon juice, garlic powder, and fresh parsley in a small bowl.
Remove the biscuits from the oven and brush the tops with the lemon butter mixture right before serving.