Preheat a fan forced oven to 180C / 350F. Line two baking trays with baking paper.
To a large bowl, add both the flours, baking powder and salt and use a whisk to combine. Set aside.
To a separate large bowl add the softened butter, sugar and vanilla extract. Use an electric beater to beat until pale and creamy, about 3 minutes. Add the egg yolk and egg and beat in until well combined.
Add the dry ingredients and half the sprinkles and use a spatula to mix until a dough forms.
Use a large ice-cream scoop (about 3 tbsp) to scoop out 8 balls. Roll into balls and then roll around in the sprinkles.
Add them to two baking trays, squash down slightly and bake for 10 minutes. Allow to cool before serving.