Considering the fact that you can cook an egg with alcohol (alcohol denatures the proteins in the egg and "cooks" it), the addition of the vodka (not so much the kahlua) basically pre-cooks and curdles your eggs before the brulees even hit the oven. Once out of the oven, the curdled effect is even more apparent. There really is no reason for the vodka there in the first place. Leave it out. I would further reduce the amount of alcohol by adding less Kahlua or just substituting the Kahlua with instant espresso granules or strongly brewed coffee. You really don't want the brulees to taste like alcohol anyway, do you? I know I wouldnt.