Melt the 50g butter. I used the Thermomix @ 70, just stirring till melted. Allow to cool somewhat and then pour in the milk all at once and stir. Butter will congeal in globs.
Add the salt, sugar, and yeast to the butter and milk. Stir to dissolve a bit, and then add there flour. I set the Thermomix to knead for about 7 minutes. You don't want to heat the dough up with friction. You can use any other method to create the dough, but I'd avoid by hand which would heat up the dough.
Cover the dough and allow to rest at room temperature for about 30 minutes.
While dough rests, fold a piece of parchment so that it has an 8" square in the middle… IOW, the folded parchment should be 8 x 8
Beat the 340 grams of butter until flat.
As you flatten it, fold and turn it to make an 8" square.
Unfold the parchment paper and place the butter in the middle of the 8" square.
Following the creases in the paper, fold the butter into an 8" square again. Using the rolling pin, flatten the butter uniformly and fill the 8" square. Place in the refrigerator for about an hour.
Going back to the dough, now that it has rested for a while, shape it into a 10" x 7" rectangle and wrap it. Place it in the refrigerator for at least 2 hours. I do this overnight.
Roll out the dough to a 8 x 17 rectangle.
Place the cold butter square in the middle of the dough. Use the middle to try to reduce the dough at the ends.
Fold the two ends of the dough over the butter and seal all ends of the dough.
roll the dough out to a 24" x 8" rectangle. Fold in thirds like a letter.
Turn the dough 90 degrees and roll out again to a 24" x 8" rectangle. Fold into thirds again, wrap, and place dough in the freezer for 30 minutes.
Remove from freezer, and repeat rolling and folding. Place in freezer for another 30 minutes.
Remove and roll and fold one more time. Place dough in the refrigerator for 2 hours, store overnight, or freeze for later use.