In a saucepan, bring the stock to a simmer over medium-low heat.
In a large saucepan, cook the onion in oil over medium-low heat, stirring, until softened, for about 5 minutes. Add rice, stirring until each grain is coated with oil. Add about 3/4 cup simmering stock and cook over medium-high heat, stirring constantly, until the stock is absorbed. Continue adding stock, 3/4 cup at a time, still stirring constantly and letting each batch be absorbed before adding the next, until about 1/2 of the stock is remaining. Reduce the heat to moderate, if necessary to keep the risotto at a simmer. Continue adding the stock in the same manner until the rice is tender and creamy looking but still al dente, about 20 minutes.
Reduce the heat to low, add the butter then the cheeses. Mix well. Add the spinach and the lemon juice and continue mixing. Remove from the heat and keep warm.
In a heavy-bottomed frying pan, heat the canola oil and saute the shrimp for 2 to 3 minutes. Take the pan off the heat and immediately add the ouzo and light it. Let the flame subside. Season the shrimp with salt, and pepper, and set aside.
Garnish each portion of the risotto with grilled shrimp, parsley, lemon zest, and feta cheese.
To make veal stock:
Preheat the oven to 450 degrees F.
Remove meat from bones where possible and cut into 1-inch pieces. If using breast bones, cut apart. In roasting pan, arrange bones and meat in 1 layer, drizzle with oil, season with salt, and pepper and roast in lower part of the oven, stirring half way in between until bones are golden brown, 40 minutes to 1 hour depending on the size of the bones. Add the tomato paste by spooning it over the bones. Add the vegetables and put it in the oven for an additional hour.
Into a large stockpot, add bones, meat, roasted vegetables, herbs, and 16 cups (4 L) water. Discard fat from roasting pan. Place tray back onto the stovetop. Heat on medium for about 1 minute then remove. Immediately add 1/2 cup to 1 cup water to the pan, scraping up brown bits, put the tray back on heat and then add the deglazed liquid to the stockpot. Bring liquid to a tremble, about 190 degrees F, and cook at 190 degrees F (skim froth frequently during first hour of cooking) for 8 hours.
Pour stock in batches through a large fine sieve and discard solids. Skim off fat. (Alternatively, cool stock, uncovered, and chill, covered. Scrape congealed fat from chilled stock.) Gently simmer stock, skimming froth occasionally, until reduced to about 4 cups (1 L), about 1 hour. Cool stock, uncovered, and chill, covered. Stock keeps, covered and chilled, 1 week or, frozen in airtight containers, 3 months. If desired, pour cooled stock into ice-cube trays with 1-ounce cups and freeze. Frozen cubes keep in heavy-duty sealable plastic bags 3 months.