Preheat the oven to 375°F. Prepare a 9x5 glass loaf pan with butter or pan-release. (If you don't have glass try and use a light colored pan as a dark pan might bake the edges too quickly.)
In a bowl add the flour, baking powder, and salt. (add the sugar here if using)
Whisk dry ingredients together.
Pour in the beer and stir all ingredients until just combined and there are no dry parts. The batter will be thick.
Pour the batter into your prepared loaf pan and smooth out if needed.
Cut the butter into slices (roughly tablespoon size) and place on top of the raw batter evenly.
Bake for 35-45 minutes or until the bread is golden brown on top. There should be about 1/2 inch of melted butter bubbling at the bottom. (I start checking at 35 minutes and my bread is usually done. I have a convection oven.)
Allow to cool on the counter for about 5 minutes or until all of the butter in the bottom of the pan is soaked back up into the bread.