Make the roux: in a small pot, combine 1/2 cup milk, 1/2 cup water and ⅓ cup bread flour. Cook on medium heat, whisking frequently until it becomes a thick paste. Remove from heat and set aside.
Make the dough: Heat the other 1/2 cup milk until it’s warm but you can comfortably stick your finger in it. Whisk in the yeast and set aside until foamy.
In the bowl of a stand mixer fitted with a dough hook, combine the roux, milk & yeast mixture and remaining dough ingredients. Knead until the dough comes together in a soft mass, at least 5-7 minutes – it will still be sticky. Place the dough in an oiled bowl and cover with plastic wrap and a tea towel. You can either place it in the fridge for an overnight rise or you can leave it at room temperature for 1-2 hours, until it’s doubled in size.
Make the caramel sauce: In a pot, combine the sweetened condensed milk, golden syrup and butter and cook on medium, whisking constantly to prevent milk from scorching, until it thickens and turns a few shades darker. This can take 10 minutes or more. Reduce the heat to low and add the salt and vanilla, whisk to combine and then add the heavy cream and chocolate. Remove from heat and set aside to cool.
Oil two loaf pans and line with parchment paper.
Once the dough is doubled in size, dump it onto a lightly floured counter. Divide it in half. Working with one half at a time, roll out the dough to a 13×9 inch rectangle. Spread with 3/4 cup of the caramel ganache, sprinkle on some flaked sea salt, and half of the pecans.
Roll up the rectangle from the shorter side, into a log. If the caramel was very runny when you spread it, let the log sit in the fridge or freezer until a bit firm (this way it won’t be very messy when shaping). Cut off edges and slice the log down the middle into two halves. Twist them around each other. Alternatively slice into 4 strands and braid.
Repeat with other half of dough and set in prepared loaf pans. Set in a warm place for a second rise, about 45 minutes if the dough was at room temperature when you started working with it or an hour and a half if it was cold. The dough should be puffy but not bubbly.
Preheat the oven to 350 F. Brush an egg yolk whisked with a bit of water on the loaves, avoiding the ganache. Give each loaf an aluminum foil ‘tent’ (draping it over the pan very loosely) so it doesn’t overbrown. Bake the loaves for 25 minutes then remove the tent, bake for another 10 until a thermometer reads 190 F or you press the center and can’t detect any doughiness.