1. Combine Wet Ingredients and Starter: In a large mixing bowl, gently whisk together the active sourdough starter, warm water, maple syrup, melted butter, and salt until well combined. The mixture should look slightly milky and uniform.

2. Add Oats and Flour: Stir in the rolled oats, then gradually add the bread flour, about a cup at a time, mixing with a wooden spoon or your hands until a shaggy dough forms. It will be sticky at this stage, but don’t worry.

3. Knead the Dough: Turn the dough out onto a lightly floured surface. Knead for 8-10 minutes until the dough becomes smooth and elastic. It should pass the “windowpane test” – you should be able to stretch a small piece thin enough to see light through it without tearing.

4. First Rise (Bulk Fermentation): Place the kneaded dough into a lightly oiled bowl, turning it once to coat. Cover the bowl with plastic wrap or a damp kitchen towel. Let it rise in a warm spot for 4-6 hours, or until it has visibly increased in size and looks bubbly. The exact time will depend on your starter’s activity and your kitchen temperature.

5. Shape the Loaf: Gently turn the dough out onto a lightly floured surface. Deflate it slightly and shape it into a tight log or oval that will fit into your loaf pan. You want to create good surface tension to help with the final rise and oven spring.

6. Second Rise (Proofing): Place the shaped dough into a greased 9×5-inch loaf pan. Cover it loosely with plastic wrap or a damp towel and let it proof for 1-2 hours, or until it looks puffy and has nearly doubled in size. A gentle poke with a floured finger should leave a slight indentation that slowly springs back.

7. Prepare for Baking: Preheat your oven to 375 F (190 C) with a rack in the center. If desired, brush the top of the loaf with milk or melted butter for a softer crust, or leave plain for a crisper crust. You can also sprinkle a few more oats on top for decoration.

8. Bake the Bread: Bake for 35-40 minutes, or until the crust is golden brown and the internal temperature reaches 200-210 F (93-99 C) when measured with an instant-read thermometer. If the top is browning too quickly, you can loosely tent it with aluminum foil.

9. Cool Completely: Remove the loaf from the pan immediately after baking and place it on a wire rack to cool completely before slicing. This is crucial for the crumb to set properly and prevent a gummy texture. It usually takes 1-2 hours.