Step 1: Prepare the Dough
In a large bowl, combine warm water, warm milk, and sugar. Sprinkle in the yeast and let it sit for 5–10 minutes until foamy.
Add flour, salt, egg, and softened butter. Mix until a rough dough forms.
Knead by hand or with a stand mixer for 6–8 minutes until smooth and elastic.
Shape into a ball, place in a lightly oiled bowl, cover, and let rise in a warm spot for 1 hour or until doubled in size.

Step 2: Make the Butter Block
On a sheet of parchment paper, arrange cold butter slabs into a square (about 7×7 inches).
Place another piece of parchment on top and gently pound and roll until even.
Chill the butter block in the fridge until firm but pliable.

Step 3: Laminate the Dough
Once the dough has risen, roll it out on a floured surface into a 10×10 inch square.
Place the chilled butter block in the center at a 45° angle (like a diamond shape).
Fold the dough corners over the butter to completely encase it like an envelope.
Roll the dough out into a long rectangle (about 8×20 inches).
Fold it into thirds like a letter, wrap in plastic wrap, and chill for 30 minutes.
Repeat the rolling and folding process two more times, chilling between each set. You’ll have completed three folds total.

Step 4: Shape the Loaf
After the final chill, roll the dough into a rectangle about 9×14 inches.
Fold into thirds one last time, then roll lightly until the width fits your loaf pan.
Place the folded dough into a greased or parchment-lined loaf pan.
Cover lightly and let rise at room temperature for 1–1.5 hours until puffed and nearly doubled.

Step 5: Bake the Croissant Loaf
Preheat your oven to 375°F (190°C).
Whisk together the egg and milk for the egg wash. Brush the top of the dough gently.
Bake for 35–40 minutes, or until the top is deep golden brown and the loaf sounds hollow when tapped.
Let it cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.