- Rehydrate your raisins at least 12 to 24 hours before you plan to make your pains au raisin. Stir together the raisins, water, and Cognac. Store the mixture in the refrigerator until use.
- Dissolve the yeast in the warm water for 5 minutes. Add the bread flour, milk, sugar, melted butter, and salt to the dissolved yeast and water and mix the dough on medium speed for about 2 minutes. If the dough is too sticky, add 1 tablespoon of extra flour at a time, until the dough is just firm enough to fold a shape.
- Shape dough into a ball and loosely cover it with plastic wrap. Allow it to rest at room temperature for 30 minutes. Roll the dough into a 10-inch by 15-inch rectangle, and then cover it loosely and allow it to rise for 40 minutes.
Brush the rectangle with the softened butter and then fold the dough into thirds, like a letter. Roll the long, thin rectangle back into the original 10-inch by 15 shape. Fold the dough into thirds, again, and then cover the dough with plastic wrap and allow it to rest in the refrigerator for 1 hour. Repeat this process one more time.
- Roll the dough into a 25cm by 75cm rectangle and spread the frangipane across the surface of the rectangle. Drain the raisin, discarding the soaking liquid, and evenly scatter them over the surface of the almond filling. Roll the dough into a log and cut it crosswise into 18 slices. Arrange each slice on a lightly greased baking sheet with at least 2 inches between each pastry. Cover them loosely with plastic wrap and allow them to rise for 1 hour to 90 minutes, until they are nearly doubled in size.
- Preheat the oven to 180C. Whisk the egg and 2 tablespoons milk together to make an egg wash. Brush the egg wash across the surface of each pastry. Bake the pains au raisin for 14 to 16 minutes, until they are puffed and golden brown.