My mom used to make a delicious lamb sauce with cubed lamb shoulder. I searched the internet for lamb ragu, and most were made with ground lamb. The closest recipe I could find was in my own cookbook, Bugialli on Pasta, by Giuliano Bugialli.
Here is what I did for one huge lasagna pan:
3 lbs lamb shoulder (cut and trimmed by my butcher)
2 large red onions, peeled and chopped
several sprigs of rosemary, chopped
4 oz. pancetta, chopped
1/4 c. olive oil
1/2 c. dry red wine
3 T. Italian tomato paste (double or triple strength)
2 c. chicken or beef broth
salt, pepper and red chili flakes to taste
Cut lamb into one inch cubes and set aside. Heat olive oil in a large dutch oven, or pot. When oil is warm, heat onion, pancetta and rosemary for about 10 minutes.
Add lamb and cook 5 more minutes. Pour in wine and let simmer for 5 minutes to let wine evaporate. Stir tomato paste into broth and add to pot. Season to taste with salt, pepper and red chili flakes. Simmer, covered, for 1 hour. Remove lid, increase heat and cook a few more minutes until sauce is thick and ready for pasta or lasagna.
For lasagna: I alternated layers of thin homemade pasta sheets with bechamel sauce and lamb ragu. I also alternated with two extra rich layers of a mixture of 16 oz. marscapone and 2 c. grated gruyere. I froze the lasagna uncooked, thawed it the night before the party, and baked it at 350 for 45 minutes. Let it set for 10 min. before serving.
The day we made lasagna, we wanted a sample, so with our extra pasta dough, we had just enough sauce, filling, and bechamel to make two small ramekins, and get a preview.
We decided this was good enough to serve company. I have another whole pan in the freezer!