Arrange all the dipping ingredients on a large platter or wooden board. Put the pickle in a small wide dish.
In a bowl, combine the grated cheddar with the cornflour and mustard powder and toss well together.
Rub the garlic clove vigorously around the inside of a saucepan – a cast iron saucepan is ideal – or a fondue pot. Pour the beer into the saucepan and bring to a very gentle simmer over a low heat.
Add the cheese, one handful at a time, stirring well and allowing it to melt before adding more. It is important to keep stirring once the cheese is added.
Simmer gently for three minutes, stirring constantly until the fondue looks smooth and glossy. Add a little extra ale if the cheese mixture is any thicker than a pourable custard. Transfer to a burner and keep warm while the fondue is served.
Dip the pickled onions, bread and vegetables into the melted cheese to serve. Don’t double dip! Add a little pickle to each serving if you like. (If the cheese thickens a little too much while being served, add a tablespoon or two of just-boiled water and stir well.)