Preheat the oven to 180°C/fan 160°C/gas 4. Grease and line a 23cm x 23cm square brownie tin with baking paper. In a small pan, gently melt the butter, treacle, honey and vanilla paste over a medium heat, stirring to combine, then set aside to cool a little.
Meanwhile, in a large bowl, mix the remaining ingredients and add a pinch of salt. Pour in the treacle mixture, stirring with a wooden spoon until all the ingredients are well combined.
Transfer to the prepared tin, spreading the mixture evenly, then bake for 20-25 minutes. Remove from the oven, then leave to cool completely in the tin before slicing into squares to serve.