Sift the strong white bread flour into a large bowl, and add the caster sugar and active dried yeast.
Mix so they are all evenly distributed! Rub the unsalted butter into the mixture until it resembles fine breadcrumbs! (If you’re feeling lazy, then whizz these ingredients in a food processor until breadcrumbs)
Heat the whole milk gently until warm, it should just about start steaming in the pan.
Mix the whole milk and the egg into dough and mix/knead for 7-10 minutes. I use my KitchenAid with the dough hook, it only takes 7 minutes to knead! It should spring back when touched (Like a cake does when cooked).
Move to a lightly oiled bowl and cover with clingfilm, then leave in a warm place and leave to rise for 1-2 hours or until it has doubled in size (I made these on a relatively chilly day so it took the full two hours, sometimes it can take longer)!
Prep your 2lb loaf tin by buttering it and lining it with parchment paper on the bottom and the sides!
Once risen, remove the dough from the bowl and roll out onto a lightly floured work surface. I rolled mine to roughly 50cmx30cm (20″x12″).
Microwave the Nutella for about 20 seconds so it loosens and is runnier, then spread carefully onto your rolled out dough so that it’s evenly spread, but be careful not to rip the dough!
Sprinkle the chocolate chips, mini marshmallows, and crushed biscuit pieces over the top and pat down so they stick to the Nutella.
Carefully cut the dough into squares that are the size of the width & depth of your tin - for example, if your tin was 6cm deep and 8cm in width, then roughly cut them to that size, don't worry about the length of your tin, it doesn't have to be exact, as the dough will rise in the oven!
Line your squares of dough up next to each other in the tin so that they all sandwich together like sliced bread. When all the dough is in, shake it about a tiny bit so it all sits well in the tin and cover again with cling film - leave for an hour to rise again.
Towards the end of the hour for your dough rising, heat the oven to 180ºC.
Once the hour is up, bake in the oven for 25-30 minutes until golden brown on top and cooked through! Leave to cool. Remove from the tin, and enjoy!
Notes
You don't have to use Nutella - you can use whatever spread you like - but a chocolatey one works best as its melts properly! And you can use as little/many chocolate chips or mini marshmallows etc as you like - but it does make it all gooey and delicious (and super s'moresy)!
This is best eaten on the day of baking, but can be kept overnight in an airtight container at room temperature - it'll still be gooey the next day too. Or you can freeze it for up to 3 months!