Vijaya Selvaraju's Chocolate Top Tarts

Ingredients

• 2 ¼ cup all purpose flour
• ¼ cup unsweetened cocoa
• 2 tbsp sugar
• ½ tsp salt
• 1 cup cold butter, cut into small cubes
• ¼ cup milk
• ¼ cup sour cream
• ¾ cup semi-sweet chocolate chips
• 2 tbsp butter
• 2 tbsp 35% whipping cream
• ¼ tsp salt
• ½ tsp vanilla extract
• 3 tbsp powdered sugar
• 1 large egg
• 1 tbsp water
• 1 cup icing sugar
• 2 tbsp cocoa powder
• 3 tbsp milk
• Pinch of salt
• Rainbow sprinkles