Place a large skillet over medium-high heat with the butter and EVOO. Once the butter has melted, add the onions and garlic and cook, stirring frequently, for about 20 minutes, until brown and caramelized. If the edges start to get too much color, just add a little water and stir it up.
While the onions and garlic are cooking, bring a large pot of water to a boil over high heat to cook the gnocchi. Once boiling, add some salt and the gnocchi, and cook according to package directions. Remove 1/4 cup of starchy cooking liquid before draining the gnocchi and add it to the pan of onions.
Once the gnocchi is done cooking, the onions should be about ready. Drain the gnocchi and add them to the skillet of caramelized onions. Add in 1-2 handfuls of Parmigiano Reggiano – it really all depends on how cheesy you like it!! For a little added bonus and a hint of elegance, add a drizzle white truffle oil to finish it off.
In a large serving bowl, add mustard, lemon zest and juice, salt and freshly ground black pepper. Drizzle the EVOO in a slow and steady stream, whisking until combined, then add the escarole and toss until evenly coated.
Garnish each serving of gnocchi with chopped parsley and serve the escarole salad alongside.