Preheat the oven to 375 degrees F.
Melt the butter in a 12-inch enameled cast-iron skillet over medium-low heat. Add the onions and celery and saute until tender, about 5 minutes. Stir in the flour and cook, stirring, to cook off the raw taste, about 3 minutes.
Whisk together the chicken stock, creme fraiche, sherry vinegar, garlic paste and soy sauce in a medium bowl. Slowly stir the liquid into the onion mixture, whisking the entire time. Lumps might form at first but just keep whisking -- they will go away. Lower the heat to medium-low and continue to cook until the sauce simmers and is thick enough to coat the back of a spoon. Stir in the chicken, rice, broccoli rabe, rosemary, liquid smoke, red pepper flakes and cheese. Top with the sliced almonds and bake until golden brown, 15 to 20 minutes.