First, let me warn you that Kahlua has a massive 17g of carbs per 1oz shot. It is VERY full of sugars. Milk can also be high in sugar in its natural state, up to 12g per 1 cup glass. Vodka has 0g of carbs, but you're already doomed with the other 2 ingredients :)
Luckily, coffee is zero carb. In essence, a recipe for homemade Kahlua is coffee, sugar, vanilla and brandy. We can use Splenda for sugar, and brandy is 0g carbs. Vanilla is pretty much 0g at the amounts used. So the key to making this a low carb recipe is to create your own Kahlua and use that.
1/4 cup STRONG brewed coffee
1/4 cup Splenda
1 tsp vanilla
2oz (1/4 cup) low carb milk
Make your favorite coffee, but be sure that it's strong. Pour out 1/4 cup into a mixing bowl. Blend the Splenda and vanilla into this. Feel free to substitute in other sugar alternatives if you wish.
Next, cool this mixture down. You can do this quickly in the freezer, or toss some plastic ice cubes into it. Once it's cool (maybe 5 minutes or so) mix in the vodka, brandy and milk.
The brilliant part of this is you get maybe about 1g from the low carb milk, and that's really it! So you save a TON of carbs by making it yourself, plus it's far cheaper and yummier!
Carb Count: just figure out what 1/4 cup of your favorite low carb milk is, and that's it!
Lisa Shea's Library of Low Carb Books