Preheat oven to 375 degrees. Butter a loaf pan and line it with parchment paper. 

In a medium bowl, whisk together the flour, baking powder, salt, and sugar. Pour in the beer and stir just until ingredients are fully combined and there are no pockets of flour. 

Scrape the batter into the prepared loaf pan, smooth the top to even it out, and pour the melted butter on top. Bake for 55-60 minutes, until the top is domed and golden brown and a knife or cake tester inserted in the middle of the loaf emerges clean. 

Cool fully on a wire rack before slicing. Leftovers can be wrapped first in parchment, then tightly in foil. Avoid wrapping in plastic wrap as it can make the bread overly moist and gummy.