It's appropriate that this should come back to Australia because it's evolved from the La Tartine Pumpkin Sourdough recipe in Baker:the best of international baking from Australian and New Zealand professionals by Dean Brettschneider and Lauraine Jacobs.
Pumpkins in the UK are generally only seen around the end of October for turning into Halloween lanterns. There seems to be a sales drive on butternut squash here at the moment so that's what I use. The amount of squash in the recipe is the amount of cooked flesh one small squash produced. You need to be a bit flexible about the amount of squash, the moisture it produces and the water in the final recipe. Peel the squash, cut into segments, remove the seeds and bake in a moderate oven until tender. Puree and add to the water.
I use a plain flour starter at 100% hydration (equal quantities of flour and water). This lives in the fridge and is refreshed twice before use in the following way. Remove from the fridge. Take a small amount (50g) and mix with twice the amount of water and flour (100g + 100g). Stand at room temperature for about 8 hours (morning to evening or overnight - whatever suits your programme). To this 250g add the same amount of water and flour (250g + 250g). Reduce or increase these quantities as you require, just keep the proportions the same.
Starter (twice refreshed)
You can mix and prove the dough in you usual way but since doing a Dan Lepard course 3 months ago I've gone back to hand mixing and oiling rather than flouring the work surface.
Mix all the ingredients except the sunflower seeds in a bowl until the dough just comes together. Very roughly form a ball, cover and leave for 10 minutes. Lightly coat the work surface and your hands with olive oil, scrape out the dough and kneed for 60 seconds. Form into a ball. Wash and dry the bowl, lightly oil, replace the dough and cover. Repeat this twice at 10 minute intervals.
At the end of the first hour, remove the dough from the bowl, press out to a rectangle and then gently stretch. Sprinkle sunflower seed over the surface of the dough. Fold the dough in thirds (like a business letter), turn and then stretch the other way. Sprinkle with seed, fold in three and return to the bowl, seam side down. Repeat this twice at hourly intervals, first proof total four hours.
Divide the dough into six and form into baguettes slightly less long than the width of your baking sheets. Place in improvised couches. Lay a tea towel on a board or baking sheet with a tail of a few inches hanging over the end. Flour the tea towel as you go along (rye is best). Lay one baguette at the far end and then form a corrugation so that it is separated from the second and repeat making sure everything is well floured. You will probably need to add a second tea towel to take all six. Fold the ends of the tea towels over and the sides in so that the package supports the baguettes as they rise.
Prove for about four hours, you need to judge this yourself according to temperature and starter activity. (The ones pictured were in the fridge overnight and went into the oven after an hour at room temperature.)
Roll the baguettes gently off the couches onto baking sheets. If they stick a bit, don't panic, just gently free them with your fingers, lifting the couche so that the weight of the dough helps to pull them free. Gently stretch them to the width of the baking sheets. Straighten them using a long knife or ruler, slash and bake in a preheated oven at Gas 9 (240C, 475F) for about 15 minutes then reducing the heat a little, rotating the sheets for even baking. Probably 35 minutes in total.