Dry roast the whole cloves and allspice until fragrant (approximately 1 minute), then set them to the side.
Dry roast the cinnamon stick and almond slices. Dry roast the almonds until lightly browned (approximately 3 minutes). Set them to the side with the other spices.
Transfer the ancho peppers, onion, garlic, the reserved chili water (1 cup), toasted almonds, allspice, cloves, and cinnamon into a blender. Add the crushed red pepper. Blend until smooth.
In the saucepan over medium heat, heat the oil then add the ancho pepper spice mix along with the dark brown sugar and salt. Cook, stirring often for 5 minutes.
Add the pumpkin puree and chicken broth. Stir until the pumpkin puree is fully combined into the sauce.
Add the Mexican chocolate and stir until the chocolate is fully melted.
Reduce the heat to low and cover the saucepan. Allow the sauce to simmer, stirring occasionally, for 45 minutes to an hour. Add additional brown sugar and salt to taste.
Remove the sauce from the heat and allow it to sit for 5 minutes. Serve.