Preheat the oven to 180°C.
Line a 20cm square baking tin with baking paper and grease it with some melted butter.
Blitz the biscuits and press it into the tray to make a base.
Melt the chopped chocolate, butter and vanilla together in a heatproof bowl set over a saucepan of barely simmering water, make sure the surface of the water does not touch the bowl. Once melted, remove from the heat and stir in the sugar, then leave to cool for a few minutes.
Beat in the eggs, then sift in the flour, cocoa and salt and fold in until the mixture is smooth and glossy. Break Rolo pieces into your brownie mix and combine that gently.
Pour the mixture over the biscuit base and level the top. Bake in the oven for 25 minutes or until the top starts to crack but the centre remains gooey. Turn off the oven and leave the brownies inside for a further 5 minutes before removing.
Leave to cool completely in the tin. Pop some leftover pieces of Rolo over the top of the brownies.
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