First, make the tangzhong. Mix the flour and water and heat over a low flame until it becomes a thick paste. Alternatively, you can use a microwave. Process on high for about 30 seconds, whisk, and return to the microwave, repeating until it becomes a thick paste. In thermo-mix, process at 100C speed 2 until thickened, about 3 minutes
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Add milk to tangzong and mix until smooth. (If using a TM, this can be done in the same container with butterfly). Add egg and yolk and mix till incorporated. (remove butterfly after this step if using TM).

If using a mixer, place mixture into a mixer bowl. Add flour and yeast, mixing until incorporated. (if using a TM, make sure butterfly is removed and switch to dough processing mode) Let stand for 15 minutes. Add sugar and salt and knead on low for 5 minutes (TM about 3 minutes in dough mode. Bowl friction will add substantial temperature to the dough, so I let it rest in the fridge for about 5 minutes to chill a bit.). Add butter and process for another 5 minutes, scraping down dough as needed. (TM, again about 3 minutes, with another 5 minute rest in the fridge. After the rest, I did another 10 seconds to pull it together). Move to a lightly floured counter and knead into a ball. Dough will be sticky. Transfer dough to a greased bowl, cover and let rise till doubled.

Toast the pecans if using. Whisk remaining ingredients, except the water till smooth. Add water and mix till incorporated. Grease a 9 x 13 cake pan. Pour mixture into cake pan. Sprinkle with the toasted pecans (I added some raisins too).

Mix the filling (brown sugar and cinnamon)

When the dough has doubled, stretch it out to about 18 x 12. You do not need a rolling pin for this as dough should be very extensible.

Sprinkle dough with the filling, keeping the upper 1 inch free of filling. Loosely roll up.

Measure and mark the roll into 12 equal pieces. If the roll is 18 inches (456 mm), this would be 1 1/2 inches each (about 38 mm). Cut them with dental floss. Equally distribute the buns in the cake pan.

Allow to raise until doubled in size.