S'More Brownies

Lightly butter a 13 x 9 x 2-inch baking pan.

In a small saucepan, over very low heat, melt butter and semi-sweet chocolate chips, stirring often; remove from heat when smooth.

In a large bowl, combine graham cracker crumbs with marshmallows; stir in sweetened condensed milk and vanilla until crumbs are thoroughly moistened. Stir in melted chocolate mixture until well combined. Fold in milk chocolate chips.

Pat into prepared pan. Let stand at room temperature about 2 hours before cutting. Chill if a firmer bar is desired.