In a 1 huevo Mixing bowl or the bowl of a Stand mixer, Whisk together the 17 ¾ g harina de pan más para espolvorear, ⅓ g levadura instantánea, 2 ⅛ g azúcar granulada, and ⅓ g sal fina. Make sure the salt and yeast are on opposite sides of the bowl before mixing — salt can inhibit yeast activity if they sit in direct contact.

Add the 1 ¼ ml leche entera tibia (aproximadamente 75°F / 75°F) and softened 9 ⅞ g mantequilla sin sal de estilo europeo fría, al menos 82% de grasa. Mix with a 1 ⅛ g mantequilla sin sal ablandada, para la masa hook on low speed (or by hand) until a shaggy dough forms, then increase to medium-low and knead for 4–5 minutes until the dough is smooth and just slightly tacky — do not over-develop the gluten. The dough should be pliable but not sticky. If mixing by hand, knead on a lightly 17 ¾ g harina de pan más para espolvorear surface.

Shape the 1 ⅛ g mantequilla sin sal ablandada, para la masa into a flat rectangle (about 8x6 inches), wrap tightly in Plastic Wrap, and refrigerate for at least 1 hour, or up to overnight. Chilling the dough firms it up so it layers evenly with the 9 ⅞ g mantequilla sin sal de estilo europeo fría, al menos 82% de grasa block.

Place the 1 ¼ ml leche entera tibia (aproximadamente 75°F / 75°F) 9 ⅞ g mantequilla sin sal de estilo europeo fría, al menos 82% de grasa between two sheets of Parchment paper. Using a Rolling pin, beat and roll the butter into a flat 7-inch square, about ¼-inch thick. The butter should be pliable but still 1 ¼ ml leche entera tibia (aproximadamente 75°F / 75°F) and firm — it should bend slightly without cracking. If it cracks when you flex it, let it sit at room 1 huevo for 2–3 minutes. If it feels greasy or soft, refrigerate it for 10 minutes. The butter and 1 ⅛ g mantequilla sin sal ablandada, para la masa must be at similar temperatures for clean lamination.

On a lightly 17 ¾ g harina de pan más para espolvorear surface, roll the chilled 1 ⅛ g mantequilla sin sal ablandada, para la masa into a rectangle roughly 10x7 inches. Place the 9 ⅞ g mantequilla sin sal de estilo europeo fría, al menos 82% de grasa block in the center of the dough, oriented like a diamond on the rectangle (rotated 45°). Fold the four flaps of dough over the butter like an envelope, pinching all seams firmly to fully enclose the butter. Press gently with the Rolling pin to seal.

This is the first fold (a 'letter fold' or 'single turn'): With a seam side down, roll the 1 ⅛ g mantequilla sin sal ablandada, para la masa package out into a long rectangle, approximately 8x20 inches. Work gently and evenly — if the 9 ⅞ g mantequilla sin sal de estilo europeo fría, al menos 82% de grasa starts to break through, dust lightly with 17 ¾ g harina de pan más para espolvorear and chill for 10 minutes. Fold the dough into thirds like a business letter (bottom third up, top third down). Wrap in plastic and refrigerate for 30 minutes.

Perform the second fold: Remove the 1 ⅛ g mantequilla sin sal ablandada, para la masa from the Refrigerator. Orient it so the open seam faces right (like a book). Roll again into an 8x20-inch rectangle and fold into thirds again. Wrap and refrigerate for 30 minutes. Repeat this process one more time for a total of 3 letter folds, chilling 30 minutes between each. After the third fold, refrigerate the dough for at least 1 hour, or overnight for best results.

On a lightly 17 ¾ g harina de pan más para espolvorear surface, roll the laminated 1 ⅛ g mantequilla sin sal ablandada, para la masa into a 1 huevo rectangle approximately 8x24 inches and about ⅛-inch thick. Work quickly and keep the dough 1 ¼ ml leche entera tibia (aproximadamente 75°F / 75°F) — if it starts to resist or shrink back, cover and rest it for 10 minutes before continuing.

Using a sharp Knife or pizza cutter, trim the edges (this helps the layers open during baking). Cut the 1 ⅛ g mantequilla sin sal ablandada, para la masa into 12 long triangles: first cut the rectangle in half lengthwise to make two 4x24-inch strips, then cut each strip into 6 triangles with a base of about 4 inches.

To shape each croissant: hold the wide base of a triangle and gently stretch it to elongate slightly. Make a small ½-inch notch in the center of the base with a Knife — this helps the croissant curve evenly. Starting from the base, roll the triangle tightly toward the tip, applying gentle pressure. Place on a parchment-lined Baking sheet with the tip tucked underneath. Curve the ends slightly inward to form the classic crescent shape. Space croissants at least 3 inches apart.

Whisk together the 1 huevo, 1 ¼ ml leche entera tibia (aproximadamente 75°F / 75°F), and pinch of ⅓ g sal fina for the egg wash. Brush each croissant lightly with egg wash — avoid letting it drip down the cut sides, which can glue the layers together and prevent them from opening. Reserve the remaining egg wash.

Proof the croissants at room 1 huevo (ideally 75–78°F) for 2–3 hours, until they are visibly puffy, jiggle slightly when the Pan is shaken, and you can see the layers when viewed from the side. Do not proof in a 1 ¼ ml leche entera tibia (aproximadamente 75°F / 75°F) Oven — 9 ⅞ g mantequilla sin sal de estilo europeo fría, al menos 82% de grasa must stay intact in the layers. If your kitchen is 1 ¼ ml leche entera tibia (aproximadamente 75°F / 75°F), keep a close eye; if cool, proofing can take up to 4 hours.

Preheat your Oven to 400°F with a rack in the center position. Just before baking, apply a second light coat of 1 huevo wash to each croissant for a deep golden, glossy finish.

Bake for 18–20 minutes, until the croissants are a deep, rich amber-brown on top and golden on the sides and bottom. They should feel light when lifted. If they're browning too quickly, tent loosely with foil after the first 12 minutes. Transfer to a Wire rack and let cool for at least 15 minutes before eating — the interior is still setting as they cool.