Cook the ravioli according to package directions. Drain and set aside
In a large skillet over medium heat melt the butter and oil until the butter is foamy. Add the diced onoin, rosemary, and cook on medium to medium low heat slowly until the onions begin to soften and get slightly golden.
Add the garlic, stir until garlic is fragrant but not brown. Next, add the heavy cream, bring it to a simmer and then reduce the heat all the way to low so it is at a slow gentle simmer. Add the balsamic glaze, dijon mustard chili flakes, nutmeg and salt and stir until well combined.
With the heat on low, Add in the parmesan cheese in small amounts, stirring well after each addition to ensure it melts smoothly into the sauce. Sauce should be slightly thickened from the addition of the cheese. Add in the ravioli, gently toss in the sauce and remove from heat.
Finish with arugula, freshly cracked black pepper and additional sprinkling of parmesan cheese and chili flakes. Enjoy hot!
Taste for salt and add as needed as the balsamic reduction is salty and sweet and the parmesan cheese adds salt as well. Adjust the amount of cream, balsamic glaze, and parmesan cheese based on preference of creaminess, and sweetness from balsamic.