Melt together sugar, margarine, and cocoa in a saucepan.

Remove from heat and let the mixture cool slightly.

In a large bowl, add eggs one at a time to the cooled cocoa mixture, mixing well after each addition.

Add flour, salt, pecans, and vanilla extract to the bowl and mix until just combined.

Pour the batter into a greased and floured 9x13 inch baking pan.

Bake in a preheated oven at 350°F (175°C) for 30 minutes.

Remove the cake from the oven and immediately cover the hot cake with miniature marshmallows.

Let the marshmallows melt slightly from the heat of the cake before serving.