Rhubarb-strawberry galette - Serving Dumplings

Ingredients

• 5.5 ounces all-purpose flour
• 5 ounces cold butter
• 2 tbsp sugar
• ¼ tsp salt
• 3 tbsp ice water
• 7 ounces rhubarb (cut lengthwise and into 5 cm pieces)
• 9 ounces strawberries (hulled and quartered)
• 4 ounces light brown sugar
• 2 tsp lemon juice
• ½ tsp lemon zest
• 3 tbsp corn starch
• vanilla seeds from 1/2 vanilla bean
• 2 ounces instant oats
• 1 egg beaten with 1 tsp milk (for brushing)
• coarse sugar (for sprinkling)
• vanilla ice cream (for serving)