1Put the milk into a large bowl and sprinkle the yeast overtop. Let stand for 5 minutes, until it’s foamy. Add 3 cups of the flour along with the butter, sugar, egg, cardamom, vanilla and salt. Stir until the dough comes together, and continue to knead, or mix with the dough hook attachment of your stand mixer, until the dough is smooth and elastic, adding more flour as needed (you’ll likely need 3 1/2 cups). It should be tacky, but not sticky—add more flour if it’s sticking to your hands. It will smooth out and become less tacky as it sits. Shape into a ball and place it back in the bowl, cover with a tea towel and let stand in a warm place until the dough has doubled in bulk, 1 1/2—2 hours.
2Cut the dough into two pieces and on a lightly floured surface, roll each piece out into a rectangle that’s about 9x12 inches. In a small bowl, stir together the soft butter, brown sugar and cinnamon, and spread half over each piece of rolled-out dough. Fold each piece up in equal thirds, as if you were folding a letter, and roll it again until it’s roughly 8x14 inches.
3Cut the dough lengthwise into strips about 2 cm wide. Twist each strip by holding each end and twisting in opposite directions, then holding one end, wrap it around two or three of your fingers (as if you were wrapping up an electrical cord), then tuck the end over, under and through the hole in the middle. (See video link above!)
4Place each rolled bun on a parchment-lined sheet, brush with beaten egg and sprinkle with pearl sugar or sliced almonds, and let them sit while you preheat the oven to 350?F. Bake the buns for 15-20 minutes, until golden. Makes about 1 1/2 dozen kanelbullar.