Heat milk in a saucepan to about 110 ℉. Stir in 1 tsp. of the sugar and gently whisk in the yeast. Allow to sit, undisturbed, for about 5 minutes, or until bubbly.
In the bowl of a stand mixer, with dough hook attached, add flour, sugar and salt to mixing bowl. Stir in bubbly yeast and milk mixture. Beat until dough starts to form. Add egg and egg yolk and continue to beat until blended. With the mixer on low speed, add softened butter one tablespoon at a time. Once all the butter has been added, increase to medium speed and knead until dough is smooth and no longer sticks to the sides of the bowl, about 3-5 minutes. Remove the dough from the mixer and form into a ball.
Place the dough ball into a large greased bowl. Cover with plastic wrap and allow to rest at room temperature for about 2 hours until doubled in size. Meanwhile, prepare butter block. (See instructions below) Punch down risen dough. Turn out dough onto a lightly floured work surface. Use a small rolling pin, or the palm of your hands, to gently shape dough to a rectangle about 12x8-inches. Place on a parchment lined baking sheet. Tightly cover dough with plastic wrap. Let chill in the fridge for about 30 minutes.
Place dough on a lightly floured work surface. Roll dough to a 18 x 12 inch rectangle. Place the prepared butter block towards one end of the dough, but 1 1/2 inches from the edges. Fold the rest of the dough over the butter block and press down to seal the edges, sealing the butter inside of the dough. Using a rolling pin, press firmly onto the seams of dough to seal. Roll dough to a 16 x 12-inch rectangle. If any butter escapes, tuck it back into the dough and patch to keep butter inside.
Turn dough 90 degrees and fold into thirds like a letter. Tightly cover dough with plastic wrap and place in the fridge. Allow dough to rest for 60 to 90 minutes in the refrigerator. Place dough back on floured surface. Again, roll dough to a 16x12-inch rectangle. Fold into thirds. Cover and return to fridge for 60 to 90 minutes. Place dough back on floured surface. For a third time, roll to a 16x12-inch rectangle. Fold into thirds. Turn 90 degrees and fold into thirds for the last time. Cover with plastic wrap and return to fridge for another 1 hour, or overnight.