Start by making dough

Why sourdough croissants?!?

The big advantage of sourdough for croissants is that it rises slowly and is more robust to low temperatures. That means you have less chance of screwing up and either overproofing or killing the yeast. Also, the sugar in croissants reacts nicely with the sourdough flavor to yield croissants with full robust flavor. You can't taste the sourness, it just enhances the final flavor. The sourdough croissants I've made are honestly better tasting than the croissants I've had in France.

In a large bowl, mix 1 cup active sourdough starter (pancake batter consistency) with 3 tablespoons of sugar, 1 cup warm water, and 1 1/2 cups of bread flour. [If you don't have sourdough starter, mix together a cup of flour and some warm water with one package yeast instead (add water until consistency is like pancake batter)].

Let proof 3 hours in a warm place (no need to cover). [If you substituted yeast for sourdough culture, proof 1/2 hour].

Add in 3 tablespoons of sugar, 2 teaspoons of salt, 1/2 cup of milk, and 2 cups bread flour to make a soft dough. Knead briefly, adding slightly more flour (not too much). Wrap in plastic and chill.

The photo shows the bowl with first stage of dough after being proofed for 3 hours.

(This dough recipe is inspired by the one at http://home.teleport.com/~packham/sourdrec.htm).