• Pre-heat your oven to 370℉/180℃. Line an 8x8" baking pan.
• In a small bowl, break up the dark chocolate and melt in the microwave in 20 second intervals, stirring in between to make sure it doesn't burn. Alternatively, set up a double boiler. Do this by placing a heatproof bowl over a small pot of simmering water. Add the chocolate to the heatproof bowl and stir until melted. 
• In a large mixing bowl, whisk together melted butter and both sugars until fully combined (3-5 minutes). Add in the eggs and vanilla and whisk again.
• Now, add the melted chocolate slowly and combine. 
• Add the flour, salt, cocoa powder and chocolate chip. Fold gently with a rubber spatula or wooden spoon until just combined. Pour into the lined pan.
• Bake 20 minutes, until the top looks just set but the filling may still look a little wobbly. Remove from the oven and cover in the mini marshmallows and return to the oven for 5 minutes. Remove and let cool.

For the Ganache

• Chop the chocolate up into small pieces if using block chocolate (chocolate chips are fine too). Place the chocolate in a heatproof bowl/jug.
• Heat the cream over a medium heat in a small saucepan. Once it has started simmering, pour it over the chocolate. Leave for 2 minutes, then whisk to create a thick, glossy chocolate ganache. Stir in the slivered/sliced almonds.
• Spread the almond ganache over the brownies. Let set before slicing and serving (speed up this process by placing in the refrigerator).