Three Chimneys: Shortbread

I've actually made this recipe before. When I first bought the book, I wanted to try out one of the recipes. In need of some biscuits for the week, this is the one I chose. At the time , I didn't have the rice flour the recipe uses, so I used all plain flour (actually, type OO plain flour). They came out fine.
This time, I did have rice flour - although it was brown rice flour, not the white specified in the recipe. The butter was Graham's Gold - and the butter isn't just Gold in name. As the two main ingredients in the shortbread are the flour and the butter, I figured it was worth using a really good butter.
So how did they turn out this time? Well, I don't know if it was because the kitchen was warmer, or the butter was fattier, but I had more trouble with the dough. This time I had to chill it before I could roll it out and cut it cleanly. I slightly overfired the first tray. But the rest came out very well - light, crumbly, slightly flaky inside. Having had two successes with this, I think I might need to start experimenting with additions.