For dough:Start by preparing  your flour paste or tangzhong: combine water, milk and flour in a small saucepan set over medium heat. Whisk gently until no clumps remain. Continue to whisk until the mixture thickens to the consistency of thick paste, about 2 to 3 minutes. Remove from heat.Add cubes of butter to still-warm saucepan with flour paste and gently whisk until melted and smooth, then whisk in milk. Add in the egg yolks and whisk until fully incorporated. At this point the mixture should feel lukewarm to the touch.In the bowl of a stand mixer fitted with the dough hook, whisk together the flour, powdered milk, and yeast to combine. Pour in the lukewarm flour paste, and mix on low speed until mixture forms a shaggy dough, about 1 to 2 minutes. Cover bowl with plastic wrap and let rest for 20 minutes (this rest gives the flour a chance to absorb the liquid, making it easier to knead later).Remove plastic wrap and add the sugar and salt. Mix on medium-low speed until dough is smooth and elastic, but still somewhat sticky, about 10 minutes. Add more flour only if absolutely necessary (a softer initial dough will result in a softer final product).Shape the dough into a ball (lightly oil your hands if necessary) and place in a lightly greased bowl. Cover with plastic wrap or a kitchen towel and allow to rise in a warm place until doubled in volume, about 1 to 1 1/2 hours. Alternatively, if you want to bake your rolls the next day, tightly cover the bowl with plastic wrap and pop it in the refrigerator to rise slowly overnight (my preference, as cold dough is so much easier to work roll out and shape).For Topping:Melt butter in a small saucepan over medium heat. Add brown sugar, salt, and spice mix and stir until smooth and paste-like (it may appear slightly separated, that’s ok).Remove from heat. Whisk in syrup and heavy cream until smooth, followed by rum. Set aside and let cool to lukewarm (topping can also be made the day ahead of time, cover and refrigerate until ready to use, and return to room temperature before using).To Assemble:Lightly butter a 9-inch square cake pan.In a small bowl, whisk together brown sugar and remaining half packet of spice drink mix and set aside.Turn dough out onto a lightly floured work surface. Pat into a rectangle, then roll out evenly into a rectangle approximately 10 inches tall by 13 ½ inches wide. You want this piece to have an even overall thickness, with as square edges as possible.Soften butter until it is nearly melted; it should be the consistency of warm peanut butter. Using a pastry brush, spread a thick layer of butter evenly over the entire piece of dough.Sprinkle an even layer of filling over butter, leaving a 1-inch space empty along the top long edge. Pat down filling to adhere it. You can also gently run a rolling pin over the surface to compress the filling into the dough, making it easier to roll up.Working with the long edge nearest you, start to roll up the dough fairly tightly, taking care not to stretch out the ends too much. Pinch along the edge of the dough to seal the seam, then roll the seam so it is face down.Using a ruler, measure out where you will cut your rolls, using a small knife to mark the cuts. I cut my log into 9 rolls each 1 ½ inches wide.To cut the rolls, you can use a sharp serrated knife (try to cut cleanly through in one movement front to back, rather than sawing it back and forth). You can also wrap a piece of unflavored dental floss or sturdy thread around the dough, which will create perfect, clean cuts.Pour cooled topping mixture into prepared cake pan. Sprinkle evenly with chopped pecans.Place rolls into pan, leaving an even amount of space between rolls and between the edges of the pan. Lightly cover and set pan in a warm spot (I like to use my oven with the light on) until rolls are noticeably puffed and just touching one another, about 30 to 60 minutes.While rolls are rising, preheat oven to 350 degrees F.Once rolls are nearly doubled in size, bake for 30 to 35 minutes, or until tops are lightly golden brown and filling is bubbly (to be precise, the center of the center roll should read about 190 degrees F on an instant-read thermometer). If your rolls are browning too quickly, you can tent them with foil and return to the oven to continue baking.Remove rolls from oven, and immediately (and carefully!) invert onto a rimmed platter or baking sheet, or a cutting board with a groove to catch the excess caramel. Be very careful doing this as the caramel is extremely hot; I find using some silicone-grip oven mits to be very helpful.Let rolls cool slightly before serving. Rolls also reheat beautifully; keep covered in the refrigerator then rewarm for a few minutes in the oven or a few seconds in the microwave before serving.