Blueberry streusel muffins

Ingredients

• 125g unsalted butter, melted and cooled
• 2 eggs, beaten
• 125ml milk
• 1 tsp vanilla extract
• 250g plain flour
• 200g caster sugar
• 2 tsp baking powder
• 200g blueberries
• Pinch of salt
• 2 tbsp plain flour
• 2 tbsp light brown soft sugar
• 1 tbsp caster sugar
• 1/2 tsp ground cinnamon
• 1/4 tsp ground nutmeg
• 1/4 tsp mixed spice
• 30g cold unsalted butter
• 2 tbsp rolled oats