1. 1. Prepare Your Dough Mixture: In a large mixing bowl, combine the sourdough discard, granulated sugar, melted butter, and vanilla extract. Whisk these ingredients together until they are well combined and smooth. This forms the wet base for your dough.

2. 2. Combine Dry Ingredients: In a separate medium bowl, whisk together the all-purpose flour, baking powder, baking soda, and salt. Make sure there are no lumps and the leavening agents are evenly distributed throughout the flour.

3. 3. Form the Dough: Gradually add the dry ingredient mixture to the wet ingredients, alternating with the milk. Mix until a soft, shaggy dough forms. Once combined, turn the dough out onto a lightly floured surface and knead gently for about 2-3 minutes until it comes together into a smooth ball. Avoid over-kneading, as this can make the dough tough.

4. 4. Roll and Fill the Dough: On a lightly floured surface, roll the dough into a large rectangle, approximately 10×14 inches. Aim for an even thickness. Arrange the sliced strawberries evenly over the dough, leaving about a 1-inch border around the edges. Sprinkle the chocolate chips over the strawberries.

5. 5. Shape the Stromboli: Starting from one of the longer sides, carefully roll the dough tightly into a log. Pinch the seams together to seal the edges and tuck in the ends to prevent the filling from escaping during baking. Transfer the stromboli to a baking sheet lined with parchment paper.

6. 6. Bake to Golden Perfection: Brush the top of the stromboli lightly with a little extra melted butter or milk, then sprinkle generously with turbinado sugar. Bake in a preheated oven at 375 F (190 C) for 20-25 minutes, or until the stromboli is golden brown and cooked through. The sugar on top should be caramelized and glistening.

7. 7. Cool and Serve: Once baked, remove the stromboli from the oven and let it cool on the baking sheet for 5-10 minutes before transferring it to a wire rack. This allows the filling to set slightly. Slice into thick pieces and serve warm, optionally dusted with powdered sugar.