Prep pan: Grease a 8x8'' baking pan with non-stick cooking spray or butter (or use 4 mini disposable loaf pans, for gifting).

Cut marshmallows (we use scissors, dipping them in water after each cut, to keep the marshmallow from sticking). Add cut marshmallows to the pan.

Melt Chocolate: In a saucepan over low heat (or a double boiler) add chocolate and butter. Stir constantly until melted and smooth. Remove from heat and add vanilla extract and walnuts, if using.

Slowly drizzle melted chocolate over marshmallows, gently nudging between the marshmallows as you go, so that the chocolate seeps into all of the cracks.

Refrigerate until set. Store leftovers in the refrigerator for up to 2-3 weeks.