In a large glass bowl, mix together the ingredients for the levain.

Cover with plastic wrap and leave at room temperature overnight (or for 12 hours).

In the bowl of your stand mixer, combine the bread four, milk, egg, sugar, salt, and the 41 grams of room temperature butter.

Add in the levain from the night before.

Knead the dough with the dough hook on low speed for 3 minutes, until gluten formation starts, and then on medium speed for 3 minutes.

The dough should be slightly elastic, tacky to the touch, and fairly smooth.

Cover the bowl with plastic wrap and allow to proof for 3-4 hours, until puffy.

Place the dough in the fridge overnight.

Prepare the butter block. Between two pieces of parchment paper, tap and roll the dough to shape it into a 7.5" square.

Cover with plastic wrap and chill for 1 hour or overnight.

Take the chilled dough out of the fridge and roll in on a lightly floured surface to an 11" square.

Place the butter in the middle of the dough so that it forms a diamond.

Fold the corners of the dough over so it encloses the butter.

Roll the dough out into an 8"x16" rectangle – make sure you always roll from the middle out to evenly disperse the butter.

Trim the short edges of the dough to expose the butter layer and even the sides (the neater your edges the better your layers will be in the final dough).

Fold the bottom third of the dough up and the top third down, like a letter, keeping the edges even together.

Wrap the dough in plastic and place in the fridge for 1 hour.

Roll the dough out to an 8"x16" rectangle.

Trim the short edges so they are even.

Fold the dough into thirds (bottom up and top down).

Wrap in plastic and chill for 1 hour.

Roll the dough into an 8"x16" rectangle.

Trim the short edges even.

Fold the dough into thirds, bottom up and top down).

Wrap in plastic and chill for 1 hour.

Roll the dough out to an 10"x16" rectangle.

Cut the rectangle in half lengthwise.

Roll each half to a 9"x18" rectangle.

Trim all the edges neatly to expose the butter layers, then cut each half into 3 smaller rectangles.

Cut each rectangle diagonally to get 6 triangles.

Roll each triangle as tightly as you can (starting with the wide edge and ending with the point).

Place each roll on a cookie sheet (with the point underneath), cover with plastic wrap and allow to rest for 2-3 hours. They are fully proofed when they jiggle a little when you gently bump the pan.

Preheat the oven to 425F.

Take the reserved portion of beaten egg and brush over the tops of the rolls.

Bake the rolls for 10 minutes.

Turn the oven temperature down to 375 and bake for another 15 minutes.