In a large skillet, heat butter over medium heat. Add celery and onion and stir until translucent and soft, about 3 minutes.Add garlic and flour, whisking to combine. Continue to whisk as you pour in the evaporated milk and whisk until fully combined. Season with salt and pepper to taste.Cook the sauce until thickened, about 2-3 minutes.Pour sauce into slow cooker and add chicken broth and broccoli. Stir to combine. Cook on high for 3 hours or on low for 6 hours.Turn off heat and stir in cream. Stir in all the cheese (in batches) stirring to melt and combine.Serve hot garnished with sour cream, cilantro, and more cheese if desired.Enjoy!