– ½ cup 1 stick softened butter – ⅔ cup brown sugar packed – 2 large eggs at room temperature – ½ cup plain Greek yogurt or sour cream – 2 tsp pure vanilla extract – ⅓ cup milk of choice* – 2 cups gluten-free all-purpose flour – 1 tsp baking soda – 1 tsp baking powder – 1 tsp sea salt – 1 ½ cups fresh blueberrie Streusel Topping (Optional): – ⅓ cup gluten-free all-purpose flour – 2 Tbsp brown sugar – 1 Tbsp ground cinnamon – 3 Tbsp melted butter – Pinch sea salt