Hail and blessed be the hour and moment in which the Son of God was born of the most pure Virgin Mary, at midnight, in Bethlehem, in piercing cold. In that hour, vouchsafe, O my God! to hear my prayer and grant my desires (mention your intentions here), through the merits of Our Savior Jesus Christ, and of His Blessed Mother. Amen.
If you're wondering what St. Joseph is doing here, this short caption from the Web Gallery of Art may enlighten you:
The iconography of St Joseph in the Nativity panel is unusual. What we find here is the story of 'Joseph's stockings'. Jesus' father sits at the bottom of the panel, cutting up one of his leggings. Certain Middle Dutch and German Christmas carols tell that the Christ Child was swaddled in cloth cut from this undergarment. Aachen Cathedral once owned a relic said to be 'Joseph's Stockings', which were the subject of intense veneration in around 1400. It is likely, therefore, therefore, that this little panel was produced in the Aachen area (or at least the region between the Meuse and Rhine), probably some time around 1400.