Preheat an oven to 400 degrees.
In a large skillet preheated to medium-high heat add a splash of olive oil along with ground beef. Cook the ground beef until it is no longer pink, about 5 to 7 minutes. Remove the beef with a slotted spoon and place it in a bowl. Set aside.
In the same skillet as the ground beef, leave about 1 tbsp of rendering in the skillet. Add in the shallots, garlic, kosher salt, pepper and cook over medium-high heat. While the shallots cook, combine pumpkin puree, whipping cream, sage, rosemary, thyme, egg and ½ cup Monterey jack cheese in a bowl. Once the shallots are golden, about three or four minutes, add the pumpkin mixture to the skillet.
Gradually whisk in the chicken stock. Add more chicken stock if you feel the sauce is too thick. Once the sauce has reached your desired consistency, add the reserved ground beef. Toss the ground beef with the sauce.
Pour ⅓ cup of the pumpkin sauce on the bottom of a 9 x 13 baking dish. Next, fill a tortilla with the ground beef mixture. Place the tortilla seam side down in the baking dish. Repeat until all the pumpkin mixture has been used. Once you have filled the baking dish, pour the remaining sauce over the top of the tortillas. Top with 1 cup shredded cheese. Bake uncovered for 30 minutes or until warmed through and the cheese has melted. Garnish with additional herbs if desired.