Gluten-free custard-filled doughnuts

Ingredients

• 3 cups gluten-free plain flour
• 1/2 cup cornflour
• 1/2 cup white rice flour
• 1/2 cup gluten-free self-raising flour
• 2 tsp dried yeast
• 1/4 cup caster sugar
• 3 eggs
• 180 g butter, melted
• 1 tsp vanilla essence
• 1 1/2 cups milk
• Cooking oil spray
• Vegetable oil, to deep-fry
• Custard filling
• 1/2 cup sifted gluten-free icing sugar
• 1 2/3 cups thick vanilla custard