In a nonreactive medium sauce-pan, warm the olive oil. Add the escarole and cook over high heat, stirring, until wilted. Reduce the heat to moderate, add the garlic and stir for 2 minutes. Stir in the anchovy fillets and oil; reduce the heat to moderately low. Cover and cook, stirring twice, until the escarole is tender, about 4 minutes. Add the lemon juice and swirl in 2 tablespoons of the butter. Remove from the heat.