Preheat your waffle iron whilst you make the batter.
Place the butter into a jug & melt in a microwave (melt in a saucepan if you don't have a microwave) then set aside to cool slightly.
Next, place the flour, sugar, baking powder, bicarbonate of soda & salt into a large mixing bowl. Whisk together then set aside.
Add in the buttermilk, eggs & vanilla into the melted butter then whisk together.
Pour the butter mixture into the flour then whisk until just combined. Don't worry if there's a couple of lumps, we don't want to overmix the batter.
The batter needs cooking straight away!To do this, give your waffle iron's grates a spray of cooking oil, add a spoonful of batter into the centre of each one then quickly spread the batter out so that it completely covers the grates. Give the top grates another spray of oil then gently close. Cook for 4-5 minutes or until the waffles are golden brown & crispy. Serve straight away - see notes.As all waffle irons are slightly different, I'd recommend cooking one waffle first to see how much batter & cooking time is needed. Repeat with the remaining batter, making sure that the waffle iron is up to temperature before cooking.