How can I get unsweetened gluten-free chocolate brownies to hold together?

I would like to make a chocolate brownie which has no added sweetener. It would be great if it were gluten-free as well, but that is less important.

I tried a recipe from Dinah Alison's "Totally Flour-Free Baking" which had as ingredients:

140g butter, 215g sugar, 2 eggs, 75g ground almonds, 4 tablespoons of cocoa powder, 200g chocolate, 85 g walnuts, 1/2 tspn of vanilla essence and 50g choc chips.

I adapted this by losing the sugar, replacing the choc chips with more walnuts and using pure "cacao" from this site:

http://williescacao.com/fine-chocolate/products/

The result was quite nice to eat, but much, much too crumbly. The brownies just had no cohesion.

I tried a second attempt by adding cocoa butter - figuring that I hadn't got enough fat in - but that didn't help much, and the cocoa butter made it less chocolatey.

What am I doing wrong? I suspect that maybe her recipe doesn't have enough egg, but is there anything else I should adjust?

Note that its really important there's no sweetener. "Sugar-free" recipes on the net all seem to have something else - bananas/dates/sucrulose/apple mash. The recipe above is as sweet as I ever want it to be.

Edit: the flour-free nature of the recipe is a plus but not vital. If I can get a plausible sugar-free brownie working then I can worry about the flour later.