Line a plate with paper towels and spread ricotta cheese evenly. Place another paper towel on top and pat down to absorb excess moisture. Remove the paper and scrape cheese into a bowl; set aside.
In a large bowl, pour can of tomatoes and using hand, crush them; set aside.
In a large bowl, combine mashed potatoes, egg yolk, ricotta, salt and ½ cup flour; stir to combine before adding the remain flour and mix again.
On a very well-floured work surface, dump potato mixture. Add more flour and knead until no longer sticky (add as much flour as needed). Shape into a ball and divide by 4. Roll a ¼ at a time into a long tube of 1-inch, doing a back and forth motion by putting a little pressure on the middle and working way out. Flour cutting tool and cut dough into 1-inch. With the back of a fork, press down or use a finger/thumb. Place gnocchi on a large baking sheet lined with silpat or wax paper and transfer to the fridge for 30 minutes.
In a large deep saucepan over medium, heat oil. Add onions and sauté for 2 minutes. Add garlic and sauté for 1 minute. Add red pepper flakes and quickly sauté for 30 seconds. Pour crushed tomatoes and bring it to a boil. Add Italian seasoning, reduce heat to medium-low and simmer gently for 10 minutes.
Add ricotta cheese to sauce and stir until very well incorporated; simmer for 10 minutes. Add heavy cream, stir and simmer for another 10 minutes. Keep sauce warm until ready to serve.
Bring a large pot with salty water to a boil. Drop gnocchi in and as soon as they rise, they’re ready. Remove from the water and transfer them in the sauce. Stir until gnocchi are well coated. Spoon into a plate and sprinkle Parmesan cheese on top. Makes 80 gnocchi.