Summer berry galette recipe

Ingredients

• 200 g plain (all-purpose) flour
• 100 g cold butter
• 2 tbsp icing sugar
• 1 tsp vanilla extract
• 1 egg, mixed with 1tbsp cold water
• 1 egg yolk, to glaze
• 2 tbsp brown sugar
• 350 g blueberries, plus an extra handful to serve
• 100 g blackcurrants
• 2 tbsp fresh lemon juice
• 1 tsp cornflour
• 3 tbsp brown sugar