1. 1. Combine Wet Ingredients and Starter: In a large mixing bowl, combine the warm milk, granulated sugar, and active dry yeast. Stir gently to dissolve the sugar and yeast, then let it sit for about 5 minutes until the yeast becomes foamy. This indicates your yeast is active. Next, add your sourdough starter (active or discard) and the melted butter to the mixture, stirring until well combined.

2. 2. Add Dry Ingredients to Form Dough: Gradually add the all-purpose flour and salt to the wet ingredients. Mix with a wooden spoon or your hands until a shaggy dough forms. It will be sticky, but don’t worry. Once combined, turn the dough out onto a lightly floured surface.

3. 3. Knead the Dough Until Smooth: Knead the dough for 5-7 minutes. The dough should become smoother and more elastic, though it will still be soft. Avoid adding too much extra flour during kneading, as this can make the focaccia dense. A slightly sticky dough is what you’re aiming for.

4. 4. First Rise (Bulk Fermentation): Lightly grease a clean bowl with a little olive oil. Place the kneaded dough in the bowl, turning it once to coat. Cover the bowl with plastic wrap or a clean kitchen towel and let it rise in a warm place for 1 to 2 hours, or until it has roughly doubled in size. The exact time will depend on the warmth of your kitchen and the activity of your sourdough starter.

5. 5. Prepare for Baking and Second Rise: Preheat your oven to 375 F (190 C). Drizzle 1 tablespoon of olive oil into a 9×13 inch baking pan, ensuring the bottom is well coated. Gently transfer the risen dough into the prepared pan. Use your fingertips to gently press and stretch the dough to fill the pan, creating those signature focaccia dimples.

6. 6. Second Rise and Baking: Cover the pan loosely with plastic wrap or a kitchen towel and let the dough rise for another 20-30 minutes while your oven finishes preheating. This brief second rise helps create a lighter texture. Once risen, remove the cover and bake for 20-25 minutes, or until the focaccia is golden brown on top and cooked through.

7. 7. Cool and Glaze: Once baked, remove the focaccia from the oven and let it cool in the pan for about 10-15 minutes. While it’s cooling, prepare the glaze by whisking together the powdered sugar, milk (or water), and vanilla extract in a small bowl until smooth. The consistency should be pourable but not too thin.

8. 8. Slice and Serve: Once the focaccia has cooled slightly, drizzle the glaze generously over the top. You can then slice it into breadsticks or squares and serve warm or at room temperature. Enjoy your sweet sourdough focaccia!