Add 1 tablespoon butter to each pumpkin half, and season with salt and pepper. Add 1 tablespoon butter to onion, season with salt and pepper and wrap in aluminum foil. In a preheated 350-degree oven, roast onion and pumpkin, cut-side up, until completely soft and somewhat caramelized, about 45 minutes.
Scoop out cooked pumpkin and place in a food processor with onion, pulsing until smooth. Adjust seasoning with salt and pepper. Transfer pumpkin puree into a bowl, add half of the toasted pine nuts and stir to combine.
Cover wonton wrappers with a damp cloth. Assemble bowl of pumpkin puree, beaten egg, pastry brush and a sheet tray dusted with flour. Lay out 1 wonton wrapper and place a heaping tablespoon of pumpkin puree in the middle. Brush around the filling with beaten egg and cover with another wonton wrapper. Press edges. Place 20 raviolis on a sheet tray and put in freezer.
In a small sauce pot, add remaining butter and cook on medium heat until the butter bubbles and turns brown. Remove from heat and add tomatoes, sage and a squeeze of lemon. Season with salt and pepper.
Cook ravioli in salted boiling water until they float. Transfer ravioli to 4 warm bowls and drizzle with brown sage butter sauce. Top with remaining toasted pine nuts.