Cook the ravioli according to the instructions on the package; drain and set the cooked ravioli aside.
While the ravioli cooks, start your brown butter by heating a small pan over medium heat. When the pan is hot, place the butter into it and let it melt. As it melts, add the sliced mushrooms and the sage; toss to coat in butter.
As the butter heats up it will start to foam. At this point, start stirring the butter, mushrooms, and sage constantly to keep the butter moving—this will prevent it from burning.
When the butter develops a golden color and gives off a rich, nutty aroma, the mushrooms should be browned and the sage should be crisped up nicely. Remove the pan from the heat, and drizzle the brown butter, mushrooms, and sage over the ravioli. Gently toss the ravioli in the brown butter and serve.