Put a large pot of water on to boil. Preheat the oven to 200°C/400°F/ Gas mark 6. Lightly grease a baking sheet.
Put about 125g/4oz of the flour, the sugar, salt, baking powder, yeast and the 2 tablspoons softened butter in a large bowl. Mix until smooth and the yeast starts to froth.
Sift in the remaining flour, and continue mixing until a stiff dough forms. Knead the dough until it is smooth and elastic. Form into a ball and allow to rise in a warm place until doubled in size.
Punch down the dough and knead for a minute or so. Divide into eight equal pieces. Roll or cut each piece into a rope 45cm/18in long and 1cm/1⁄2in in diameter, and twist each rope into a pretzel shape. Allow to rest for a couple of minutes.
Using a slotted spoon or broad spatula, slide the pretzels into the boiling water one at a time, and boil each one until they float to the top. Remove immediately, drain off and transfer to the greased baking sheet.
Bake in the oven for 15 minutes or until golden. Brush the pretzels very lightly with melted butter as they emerge from the oven. Serve warm.