Add the cubed sweet potatoes to a large pot and cover with cold water. Cover and bring up to a boil, then simmer until tender, about 15 minutes. Drain, then add to a large bowl along with the salt, brown sugar, orange zest and orange juice.
Melt the butter in a small pot on the stove top, then continue cooking for a few minutes until it turns brown and smells nutty. Add the browned butter to the sweet potatoes, being sure to scrape in all of the browned bits.
Use an immersion blender to puree the mixture until totally smooth. Alternatively, you can puree in a food processor or use a potato masher for a slightly chunkier result.
Transfer to a casserole dish or heat-proof bowl and smooth out the top. Sprinkle with toasted chopped pecans. Serve hot.