Preheat the oven to 325°F and line the pan with parchment paper or foil leaving an overhang on two sides.
Combine the butter, sugar, cocoa and salt in a heatproof bowl or saucepot.
Set the bowl atop a saucepot of simmering water to create a double-boiler. Stir the butter from time to time until it's melted and the mixture is smooth and hot to the touch. Remove the bowl from the double-boiler and set it aside to cool for 10 minutes.
Using a wooden spoon or rubber spatula, stir in the vanilla and then stir in the eggs, one at a time, stirring vigorously between each addition. Once the batter looks well-blended, shiny and thick, stir in the flour until it's fully incorporated. Spread the batter into the prepared baking pan.
Bake the brownies for 15 to 20 minutes, or until a toothpick inserted comes out with a few moist crumbs.
Remove the brownies from the oven and immediately sprinkle them with the chocolate chips, mini marshmallows and chopped almonds.
Return the brownies to the oven for about 5 minutes, just until the marshmallows begin to melt. Remove the brownies from the oven and let them cool completely on a wrack.
Using the parchment paper or foil overhang, lift the brownies out of the pan, and slice and serve.