In a large heavy-bottom pot, heat butter and garlic over medium heat until butter is foamy and garlic begins to lightly toast, about 4 minutes. Add cream, pepper flakes, salt, pepper and Worcestershire sauce and simmer. Continue to cook until liquid is reduced by about ⅓ and cream has thickened. Add kale and continue to simmer until cream thickens and kale is tender, about 8 to 10 more minutes. Check for seasoning.