Heat milk and 1 tablespoon of sugar in Thermomix bowl 2 min/37°C/speed 1. Crumble in the yeast. Let it sit for 10 minutes and then stir until the yeast is completely dissolved.
Add the remaining sugar, flour, egg, salt, cubed butter to yeast mixture. Knead 3 min/Interval. If the dough is too sticky to touch, add a bit more flour but don't over do it as it can ruin the texture. More kneading can also help bring the dough to an easier texture to work with.
Tip into a buttered bowl and cover with plastic wrap. Let the dough rise for 1 hour at room temperature.
In the meantime, prepare the filling by placing chocolate, butter and sugar into Thermomix bowl and melting together 8 min/50°C/speed 1. Stop and scrape down the chocolate so that it is all beneath the blades as it melts. Cool in the fridge until the dough is ready.
Once the dough has doubled in size, punch it to remove the air.
Preheat your oven to 180°C (350F) and butter a flat baking tray or use a bread tin of choice.
Then roll dough on a floured surface to a rectangle about 30cm x 50cm (11.8 x 19.6 inches). Spread the chocolate filling evenly onto the dough and sprinkle with the toasted mixed nuts. Carefully roll it up lengthwise.
Cut the dough lengthwise into two even pieces and braid them together with the cut facing upwards. Tuck the ends underneath.
Carefully transfer onto your prepared tray and cover with a kitchen towel. Let it rise for 30 minutes. Brush with egg wash and bake for 50 minutes.
If the top starts to become too dark, cover it with aluminum foil. Let it cool before attempting to remove it from the tray.
Do not use anything but coverture chocolate for this one. It will not taste the same with chocolate chips or an inferior chocolate that is used for baking. Use hazelnuts, pecans or walnuts, even slivered almonds. (Maybe not peanuts...IMHO!)