(Optional) Make strawberry milk by blending 112 g of whole milk and fresh strawberries until smooth. Reserve for later use.

In a stand mixer, mix flour, sugar, salt, milk (or strawberry milk), sourdough starter, water, pink food coloring, crushed freeze-dried strawberries, and optional yeast on low speed for 1 minute. Add butter and mix until a smooth dough forms (about 3-4 minutes).

Remove 20% (about 225 g) of the dough, add more pink and a bit of red food coloring to make dark pink dough, then mix until combined.

Shape both doughs into balls, place in separate bowls, cover, and let rise at room temperature for 3-6 hours. Transfer to refrigerator for a minimum of 4 hours or overnight.

To make the butter block, lay butter on parchment paper, fold over edges, beat into a ?-inch thick layer, and shape into an 8-inch square. Refrigerate to firm up.

The next day, deflate the refrigerated dough, shape into a square, wrap in plastic, and freeze for 20 minutes.

Roll the dough into a 16-inch long, 8-inch wide rectangle. Place the butter block in the center, fold over dough edges over the butter, seal, and pinch.

Rotate the dough so the seam is vertical and roll into a 24-inch long sheet, then perform the 'first turn' by folding the short ends towards the center and then folding in half. Wrap in plastic and freeze for 15 minutes, then refrigerate for 1 hour.

For the 'simple turn,' roll the dough into a 24 by 8-inch rectangle, fold into thirds, wrap, and freeze for 15 minutes, then refrigerate for 1 hour.

Roll the red dough into an 8 by 8-inch square. Dampen the top of the main dough, place the red dough on top, and roll into a 14 by 17-inch rectangle. Freeze for 20 minutes, then refrigerate overnight.

Slice dough into four 4 by 14-inch rectangles and cut each into triangles. Roll each triangle from base to tip to shape croissants and place on a baking tray, covering loosely with plastic wrap.

Proof croissants at room temperature for 4-6 hours or in a proofing box at 70F-75F for 2-3 hours until doubled in size.

(Optional) Make strawberry pastry cream by heating 1.5 cups of milk in a saucepan. Whisk together egg yolks, sugar, cornstarch, remaining milk, and salt in a separate bowl. Temper by pouring hot milk into the egg mixture, then return to the saucepan and heat until thickened. Cool, then stir in pureed strawberries.

Preheat oven to 375F. Chill croissants in the fridge for 15-20 minutes. Whisk egg yolk and heavy cream, then apply to the tops of croissants.

Bake for 15 minutes, rotate, and bake for an additional 10-15 minutes until golden brown. Cool completely.

(Optional) Fill croissants with strawberry pastry cream using a piping bag.