oooh er Anne. I have no idea why that happened. It usually rises so it cracks a little and is a nice golden brown on top. Is it perhaps because you used Xylitol rather than Splenda? When you use sugar in recipes it melts and goes liquid which Splenda doesn't, does Xylitol behave like sugar? I mean when you use Splenda in baking you have to use more liquid, perhaps that's not the case with Xylitol.
Claudia Roden has a recipe for an orange cake which set me on the trail of this one, let's see... the recipe is here http://www.lovefood.com/guide/recipes/11389/claudia-rodens-orange-and-almond-cake
I remember my first effort was this recipe but I just substituted Splenda for sugar and the result was quite dry, so then I adapted the low carb pound cake recipe using Splenda and it came out lovely.
I have people coming for dinner tonight. I have made a White chocolate and Berry cheesecake (with Splenda so it's half-way D friendly, if you don't count the Amaretti biscuits which form the base). I have also made a chocolate & raspberry brownie cake which I am worried sick over! I followed the recipe exactly (so it's anything but D friendly with 400g sugar in it) but I didn't have a rectangular cake tray, so instead between us hubby and I worked out that the area of my 23cm dia round cake tin = the area of the 20 x 30cm rectangular tin they suggested. The mixture looked a little too deep to my eye - anyway I cooked it 27 mins instead of the 20 mins suggested, but it's been out of the oven over an hour and the middle looks liquid still. Have bunged it in the fridge and hope for the best! Otherwise will freeze it and serve as a frozen dessert some other time!