Preheat the oven to 350F. Grease an 8-inch square baking pan.

Melt half the butter. In a food processor, pulse the graham crackers until they form coarse crumbs (or put them in a heavy-duty resealable plastic bag and whack them with a rolling pin.) Place the crumbs in a bowl; mix with the 3 tablespoons sugar and the melted butter until well combined. Press the crumbs into the bottom and all the way up the sides of the prepared pan. Bake the crust until light golden and almost firm, 12 to 15 minutes. Allow to cool.

In a saucepan over medium heat, melt the chocolate with the remaining butter, stirring until smooth. Whisk in the 1 cup sugar, the eggs, and vanilla. Fold in the flour and salt until just combined. Fold in the pecans.Pour the batter into the prebaked crust. Bake for 35 minutes, or until the center is just set. Top with the marshmallow creme and spread as evenly as possible. Return to the oven and bake for an additional 10 minutes. Store wrapped or in an airtight container at room temperature. The brownies will keep for 3 to 5 days.