So you took advantage of Blizzard's little Cooking leg up during Pilgrim's Bounty (don't be ashamed, I did, too), and you want to know: what's next? The holiday let you level up all the way to 350 Cooking with easily purchased vendor items, which was awesome, but cooking tops out at 450, so maybe you're wondering how to get up there. Let us help.
You may not have made it all the way to 350 during the holiday -- if you need to nab a few other points, you'll have to head to Outland and level up there for a little bit. Talbuk Steak is a good one to do if you need that extra boost -- it's vendor purchased, easily farmable (or buyable on the AH), and the Stam boost isn't bad. Once you've hit 350, then you'll need to head to Northrend. You can train at the cooking trainers in the faction inns in Dalaran. You'll probably also want to stop off and pick up the Northern Cooking quest, as Northern Stew will help you get relatively easily to 375. After that, it's time for the booze.
From 375 to 400, you'll probably want to go with Kungaloosh. There are probably other recipes that you can do (especially if you're also leveling an alt while doing this, you'll pick up lots of white food items that can help you get those leveling points), but Kungaloosh is the easiest and quickest. To get the recipe, you can do a quick quest from a drunk guy in the Dalaran sewers, and then all of the mats for cooking it can be purchased straight from the Dalaran fruit vendor. It'll go green at 387, so you'll need to cook a few extra to hit 400, but it'll get you there eventually.
After that, from 400-450, all of the recipes are bought with Dalaran Cooking Awards, done by doing the fishing or cooking dailies in Dalaran. Welcome to the recipe grind: earn some awards, buy some recipes, and grind out those last few points. Good luck! You'll be a Chef de Cuisine in no time.