In the bowl of a stand mixer, combine the all-purpose flour, granulated sugar, yeast, and sea salt. Add the cold whole milk and the softened butter. Knead on low speed for 5 minutes until a smooth, slightly stiff dough forms. Wrap tightly in plastic wrap and chill for 1 hour.

Place the cold European butter between two large sheets of parchment paper. Use a heavy rolling pin to pound and roll the butter into an exact 7x7-inch square. Chill for 30 minutes.

Roll the chilled dough into a 10x10-inch square. Place the chilled butter block in the center on a diagonal. Fold the corners of the dough over the butter to meet in the center, pinching to seal.

Roll the dough into an 8x24-inch rectangle. Fold it into thirds like a letter. Wrap and chill for 30 minutes. Repeat this rolling and folding process two more times for a total of three folds.

Roll the final chilled dough into a 10x20-inch rectangle. Trim the edges to expose the layers. Cut into slender triangles. Stretch the base and roll up tightly toward the tip.

Place the shaped croissants on parchment-lined baking sheets. Cover loosely and proof in a warm spot for 1-2 hours until doubled in size and jiggly.

Preheat oven to 400°F (200°C). Gently apply the egg wash. Bake for 10 minutes, then lower the heat to 375°F (190°C) and bake for 10-12 more minutes until they have a deep golden-brown, flaky crust.

Cool on a rustic wooden cutting board. Dust lightly with flour to enhance the freshly made feel before serving.