Step 1: Preheat your oven to 450°F (230°C). Place 115g of unsalted butter into your 8x8-inch baking dish and put the dish in the oven for a few minutes until the butter is completely melted and bubbling.
Step 2: In a large mixing bowl, whisk together 240g of self-rising flour and 30g of granulated sugar. If using all-purpose flour, ensure you have added your baking powder and salt as specified in the ingredients list.
Step 3: Gently fold in 150g of diced peaches into the dry ingredients until they are lightly coated in flour, which prevents them from sinking to the bottom of the batter.
Step 4: Pour 360ml of whole milk into the dry mixture. Use a spatula to stir the ingredients together until a wet, shaggy batter forms. Be careful not to overmix, as this will lead to tough Peach Butter Swim Biscuits.
Step 5: Carefully remove the hot baking dish from the oven. Pour the biscuit batter directly into the center of the melted butter. Use your spatula to gently spread the batter to the edges of the pan. The butter will flow over the top of the batter—this is exactly what you want!
Step 6: Use a knife to pre-score the batter into 9 squares. This helps the butter penetrate the centers and makes serving much easier later.
Step 7: Bake for 20-25 minutes, or until the tops of the Peach Butter Swim Biscuits are deeply golden brown and the butter has been mostly absorbed.
Step 8: While the biscuits bake, whisk together 120g powdered sugar, 5ml vanilla, and 15ml milk to create a smooth glaze. Drizzle the glaze over the hot biscuits immediately after removing them from the oven.