Ingredients

450g Strong White Flour
10g salt
100g active sourdough starter
300g tepid water
50g dried milk powder
40g butter, softened

Ingredients for filling

50-75g tomato base (as used for pizzas)
1 tab finely chopped olives
1 tab roughly chopped capers

Method

• Mix flour & salt together. Add everything else except the butter, mix roughly until combined, cover and leave to autolyse for 30 minutes.
• Add softened butter and work well into the dough until combined. It will be really slippery to start with but bear with it.
• Leave to prove in a covered bowl, doing a few stretch & folds every now and then, about 8 stretches each time, until about doubled in size (approx 5-6 hours).
• Gently turn out of the bowl, pre-shape and let it rest uncovered for 30 minutes.
• On a large well-floured piece of greaseproof paper, stretch dough out into a rectangle approximately 30 x 60 cm. You may need to keep carefully lifting & re-flouring under the dough as you do this. A flat-edged dough-scraper is useful if it sticks.
• Spread the tomato base thinly over the surface, leaving a strip approx 2cm wide down one long edge. Scatter other topping ingredients over the tomato base.
• Roll up from the opposite long edge, using the greaseproof paper to help roll it. If it sticks, ease it off using a dough scraper or flat edged knife. Dampen the strip that has no topping and pull it over the roll to seal it together.
• Line a 20 x 30 cm baking tray with greaseproof paper. Cut the roll into 12 pieces and stand them upright on the baking tray. Cover with baking foil and leave to prove. I prove my dough overnight in the fridge and leave it to come back to room temperature while the oven is heating up. I've also put them in straight from the fridge and that works fine too.
• Preheat oven to 250c. Turn down to 220c when you put the Stromboli in, still covered in foil. After 20 minutes remove the foil, turn down to 200c and bake for a further 30 minutes. Best eaten whilst warm but also good for picnics and they freeze well.

Variations
Experiment! Pesto can be used in place of the tomato base and most things that you might put on a pizza work well as the filling.