Base line a 20 cm (8 inch) square baking tin with baking parchment.
Preheat the oven to 180 C/350 F/Gas 4.
Weigh and mix together the flour, cocoa, almonds, baking powder and salt in a bowl. Set aside.
In a glass, heat-proof bowl, melt the butter with the 200g dark Toblerone either in the microwave (medium heat, 30 second bursts, stirring frequently) or set over a small saucepan of simmering water, stirring frequently. Set aside to cool.
In a large bowl, whisk together the sugar, eggs and vanilla until well blended (but not thick).
Add the dry ingredients to the egg mix and then add the melted chocolate. Beat with a spoon until well-combined and smooth.
Fold in the additional 80g chopped Toblerone (make sure the mixture is cool enough that the chocolate pieces won't melt when folded).
Pour the mixture into the baking tin and smooth the top.
Bake for 20 to 25 minutes until the top is firming up and a knife inserted into the centre comes out reasonably clean (a few sticky crumbs are fine).
Remove from the oven and cool completely in the tin. Refrigerate for about an hour before cutting into slices.
Bring back to room temperature and enjoy.
* Note: nutritional information is an estimate & may vary according to portion size/ingredient variants.Gluten Free Alchemist Flour Blend A can be found on the GFA Flours & Flour BlendingPage. If using an alternative flour (particularly one which is rice-based), the texture may be slightly different and more liquid may be required.