Love the doctored cake mix recipe. Friend wants an Earl Grey tea flavour cake. Should I just use some of the water called for in the recipe, make strong tea, let it cool & then continue as usual ?

that's what i would do and/or if the flavor is too light you can use a simple syrup 'splash' as well where you infuse some eg tea into simple syrup and brush or squirt it onto the baked cake --

I make delicious shortbread cookies that have the tea leaves right in the batter. I grind it up with a pestle and mortar, or you could use a coffee grinder. I add a little orange zest since it goes nicely with the earl grey. You could just add ground up tea to your batter, of course you would see the flecks, which you might not want. 

As a fan of flavored syrups, I love k8's suggestion.

Though I don't use box mix, I make a spiced chai tea cake where I steep the tea bags into heated milk and use that as a sub in my normal white cake recipe.  It has beautiful flavor.

oftheeicing -- infused milk is brilliant

Thanks K8memphis.... I love playing around with my liquids. The possibilities are endless!

YES! I do this with the cream for making ganache with orange zest, never thought of it in the cake batter. Pure genius! I love tea so much, being Canadian, I think I need to make myself an earl grey cake.