Heat your waffle maker according to manufacturer's instructions. Whisk the egg whites to stiff peaks.
In a separate large bowl, mix together the flour, bicarbonate, caster sugar and a pinch of salt. Make a well in the centre and add the egg yolks and melted butter. Start mixing with a balloon whisk; keep whisking as you slowly add the milk until you get a smooth, thick batter. Carefully fold in the egg whites with a metal spoon.
In the meantime, heat your oven to 180C/160C fan.
Use a ladle to pour the batter into your waffle maker and cook according to the manufacturer's instructions.
Repeat until all the batter has been used up, placing your finished waffles onto a baking tray as you go.
Once all the waffles are made, transfer to the oven for 5 mins to warm through and crisp.
Serve with sweet or savoury toppings - we sprinkled with icing sugar, and added strawberries and syrup.