Step 1

Whisk the ricotta, spinach, prosciutto, egg yolks, salt, and pepper in a medium bowl to blend.

Step 2

Place 1 tablespoon of the ricotta filling in the center of a wonton wrapper. Brush the edge of the wrapper lightly with water. Fold the wrapper in half point to point, enclosing the filling completely and forming a triangle. Pinch the edges to seal. Transfer the ravioli to a baking sheet. Repeat with the remaining filling and wrappers. (The ravioli can be prepared up to 2 hours ahead; cover and refrigerate.)

Step 3

Bring a large pot of salted water to a boil. Working in batches, cook the ravioli until just tender, stirring occasionally, about 4 minutes per batch. Transfer the ravioli to a large shallow bowl.

Step 4

Melt the butter in a small, heavy skillet over medium heat. Add the oregano and stir for 1 minute. Season to taste with salt and pepper. Pour the oregano butter over the ravioli and toss gently to coat. Sprinkle with the Pecorino cheese and serve.