In a medium bowl, whisk together the dry ingredients: flour, baking powder, baking soda, sugar, and kosher salt.

In another bowl, mix Dijon mustard and chilled Irish stout; chill this mixture.

Grate frozen Irish butter into the flour mixture and toss gently until coated.

Fold in the grated aged Irish cheddar until well distributed.

Make a well in the dry mixture and pour in the stout mixture; stir gently until shaggy dough forms.

Transfer dough to a floured surface and fold it over itself a few times, then pat into a 1-inch thick square.

Cut the dough into squares or rounds and arrange on a baking sheet; freeze for 15 minutes.

Preheat oven to 425°F. Brush tops of biscuits with butter and sprinkle with sea salt before baking.

Bake for 20 minutes until golden brown; cool slightly before serving.