In a medium bowl, mix together flour, water, and starter (or yeast) until it resembles a batter. Loosely cover and let sit 12 to 15 hours.

Place the 330 g of butter between between two sheets of baking parchment. Using a rolling pin, pound from side to side and shape into a block about 6 1/2 x 7 1/2 inches. Wrap tightly in parchment and refrigerate.

In the bowl of a stand mixer, fitted with the dough hook, mix together flour, sugar, yeast, and malt powder for about 15 seconds.

Pour about half the water around the poolish to free it from the bowl and add to the flour mixture. Add the butter and half the remaining water. Mix on low for 2 minutes. If the dough looks dry, add some reserved water until a dough forms. Scrape the bottom of the bowl to ensure that the flour is incorporated.

Sprinkle salt on dough and mix on low for 20 minutes. Remove dough and form into a ball. Lightly oil mixing bowl and return dough to bowl, seam side down. Cover and let rise for 1 hour.

Carefully remove dough to a work surface and pat and press to form a rectangle of dough about 10 x 7 1/2 inches. Line a baking sheet with baking parchment, and place dough in the center. Wrap with plastic and freeze for 20 minutes.

Transfer dough to a lightly-floured work surface and roll out to a rectangle 16 x 7 1/2 inches. Place butter block in the center, and fold the long edges of dough over the butter, pinching to seal.

For turn 1: Roll dough and butter out to form a 22 x 9 inch rectangle. Fold up bottom third, then fold down top third as if folding a letter. Place on parchment-lined sheet and wrap in plastic, then freeze for 20 minutes.

For turn 2: With the seam of dough to your right, roll dough and butter out to form a 22 x 9 inch rectangle, lightly dusting with flour as needed. Fold up bottom third, then fold down top third as if folding a letter. Place on parchment-lined sheet and wrap in plastic, then freeze for 20 minutes.

For turn 3: Do the same as turn 2, taking care to not let the butter break through the dough layer. Wrap and freeze for 20 minutes.

Roll dough out to form a rectangle about 24 by 9 inches, lightly dusting with flour as necessary. Cut in half to form two 12 x 9 inch rectangles. Place one on the parchment-lined sheet. Place a sheet of parchment over the dough, then place the second piece of dough on top. Wrap in plastic and refrigerate overnight.

Remove one piece of dough and place it on a lightly-floured work surface. Roll out to about 19 inches long. Trim off the ragged edges, then cut the dough in half lengthwise to make two long rectangles.

Line two baking sheets with parchment or silicone baking mats.

For croissants, cut one length of dough into six rectangles, each about 3 x 4 1/2 inches. Cut each of the rectangles in half diagonally to form triangles. Working with one triangle at a time, stretch or roll out to a length of about 6 inches. With the long point away from you, fold in the bottom two corners of the triangle, then roll tightly into a traditional croissant shape. Place on baking sheet with the point on the bottom, pressing down lightly so the croissant will not roll.

For pain au chocolat. Cut the long rectangle into about 9 rectangles, each 2 x 4 1/2 inches. Cut each rectangle in half to form a rectangle about 2 by 2 1/4 inches. Working with a piece at a time, stretch or roll to form a rectangle about 2 x 4 inches. Place 6 chocolate chips in the center, then fold the dough over from the bottom and the top, like folding a letter, and place on the baking sheet with the double layer on the bottom. Press down lightly to prevent unrolling.

Apply egg wash. In a small, bowl, whisk together egg and ice water and brush over the tops of the corissants.

Cover with cardboard boxes or plastic tubs and let proof for 2 hours.

Preheat oven to 350°F. Bake for approximately 35 minutes, or until nicely browned with no unbaked spots remaining.

You can either shape and bake the remaining dough or it can be wrapped tightly and frozen for up to a month.