Put 450 grams of the flour into the bowl of your mixer (or a large bowl, if you're doing it by hand) along with the salt, olive oil and yeast. Paul always recommends putting the yeast and salt on opposite sides of the bowl to start.
Slowly add the water and mix until the dough is pliable. You may not need all the water, so start small. Start with the mixer on low but up it to medium as everything gets incorporated. Decide whether you need the other 50 grams of flour to get the dough to the right consistency...you want it sticky and wet.
Either continue to knead (gently) in the mixer for 2-4 minutes or tip it out onto a lightly floured surface and knead by hand for 4-7 minutes.
Add the drained cherries and chocolate chips to the dough and mix slowly to incorporate. You may need to add a little more flour if the dough becomes too wet and sloppy. You DO want a wetter, stickier dough, though. I've made this at least 5 times and 3 of the times it acted totally normal, and two I had to add quite a bit more flour to make it workable...use your judgment
Assuming you've done all this in the mixer, tip everything out onto a lightly floured surface, give it a sprinkle of flour, and give it a knead by hand for just a minute, to make sure everything's mixed in evenly. Put the dough back in the bowl (or a fresh bowl), cover with plastic wrap, and leave to rest for 60-90 minutes, until doubled in size.
Once it's risen, re-flour your surface and scoop the dough back onto the counter. Punch it a bit with your knuckles to knock the air out of it, then give it a knead for a minute just to work that little bit of flour in. Cut into either two or three even pieces and form it into a two- or three-strand plait.
Dredge a baking tray with flour (or parchment paper), place the plait on it, and then place in a large plastic bag and leave to rise for 1 hour.
Preheat the oven to 400 F. Once it's finished rising, bake for 20 minutes at this temperature, then reduce the oven temperature to 375 F and bake for a further 20-25 mins, or until it reaches at least 200 F inside (I use a thermometer to check, and always check a few places in case I've hit a cherry or chocolate piece).
Transfer to a wire rack to cool, and make sure not to cut into it until it's cooled down to at least 85 F (or you'll have a doughy dense mess). Minimum 30 minutes to cool down, but probably more.