Mix together the poolish ingredients until the mixture looks like thick pancake batter. Leave this to ferment for 2-3 hours at room temperature or in a warm place (in the oven with the light on or on the proof setting should work). Once the mixture gets pretty bubbly, put it in the fridge immediately and leave to ferment overnight. If you are making the poolish on the same day as the bread, leave it to ferment at room temperature for a bit longer (3-4 hours total), then mix the dough. (But leaving it in the fridge overnight will give the final bread a better flavor, so we would recommend that!)
The next day, take the poolish out of the fridge 1 hour before mixing the dough. Let it come to room temperature (it should get even more bubbly as it warms up).
After waiting 1 hour, mix together the poolish and the rest of the dough ingredients (quick tip: use a wet spatula/dough scraper/hand to handle the sticky poolish). Add more bread/all-purpose flour if the dough is too sticky. Knead for 10-12 minutes until smooth and elastic.
Cover and let the dough proof for about 2 hours, or until doubled in size and passes the poke test (should NOT spring back immediately when poked, should spring back slightly but leave an indentation).
Oil a loaf pan (or line with parchment paper if you’re like us and your loaf pans are the opposite of non-stick).
To shape the sandwich loaf, dump the dough out on a clean surface. Using your hands, stretch it out into a rectangle, with a width equivalent to the size of your loaf pan.
Start rolling from one end, keeping the roll very tight.
Once you have rolled it up, pinch together any creases and roll the loaf against the countertop lightly to create surface tension and help close the crease on the bottom of the loaf.
Place the loaf in the pan and cover, letting this rise for another 30 minutes to an hour, or until doubled in size and passes the poke test. In the meantime, preheat your oven to 350 F (175 C).
Once doubled in size and ready to go in the oven, brush the top with a bit of milk and bake.
Bake the loaf for about 40 minutes, or until the top is a light golden brown and the bread sounds hollow when you tap it.
Let cool at least 20 minutes before slicing. Enjoy!