Preheat oven to 450°F.
Place the sliced butter in an 9×9-inch baking dish. Transfer to the oven for 5–7 minutes, or until melted and bubbling. Remove from the oven.
In a large bowl, whisk together the flour, baking powder, kosher salt, sugar, Old Bay seasoning, garlic powder, and onion powder.
Stir in the cheddar cheese and diced roasted jalapeños.
Add the buttermilk and melted butter. Stir just until combined. The batter will be thick. DO NOT OVER-MIX!
Pour the batter directly over the melted butter in the baking dish. Do not stir.
Gently spread the batter to the edges and score into 9 squares.
Bake for 28-38 minutes, or until golden brown and cooked through. Place a lined baking sheet underneath the dish to catch any butter overflow. If the tops are browning too quickly, loosely tent with foil while they finish baking.
While the biscuits bake, melt the 3 tablespoons butter in a small saucepan over low heat. Add the garlic and cook for about 1-2 minutes to remove it’s sharp-ness. Remove from the heat and stir in the Old Bay seasoning and parsley.
As soon as the biscuits come out of the oven, brush generously with the garlic butter.
Let rest for 5 minutes before serving.
