In a large bowl, whisk together the flour, sugar, yeast, and salt.

Add the lukewarm milk and melted butter. Mix until a shaggy dough forms.

Turn the dough out onto a lightly floured surface and knead for about 8-10 minutes, until smooth and elastic.

Place the dough in a greased bowl, cover, and let it rise in a warm place for about 1 hour, or until doubled in size.

While the dough is rising, prepare the butter block. Place the softened butter between two sheets of parchment paper and pound it with a rolling pin until it forms a roughly 6x8 inch rectangle.

Once the dough has risen, punch it down. Roll it out into a rectangle roughly twice the size of the butter block (about 12x8 inches).

Place the butter block on one half of the dough rectangle. Fold the other half of the dough over the butter, like closing a book. Pinch the edges to seal.

Gently roll the dough into a long rectangle, about 6 inches wide. Fold it into thirds, like folding a letter. This is the first fold.

Rotate the dough 90 degrees and repeat the rolling and folding process two more times, for a total of three folds. Chill the dough for at least 30 minutes between folds.

After the final fold and chilling, roll out the dough to about 0.25 inch thickness.

Cut the dough into 3 inch circles, and then cut each circle in half. Twist each half into a spiral to create the cronut shape.

Place the cronuts on a parchment-lined baking sheet. Cover loosely and let them rise for another 30-45 minutes.

Heat about 2 inches of vegetable oil in a deep pot or Dutch oven to 350°F (175°C).

Carefully fry the cronuts in batches for about 2-3 minutes per side, until golden brown. Drain on paper towels.

While the cronuts are cooling, whisk together the powdered sugar, milk, and vanilla extract in a small bowl until smooth to make the glaze.

Dip the cooled cronuts into the glaze, letting any excess drip off. Let the glaze set before serving.