4E is setup very well for long chains of battles, especially in the form of a dungeon crawl. However, sometimes it doesn't make sense to constantly be in chains of combat. Here are but a few examples:
The party is traveling a long road and is accosted by bandits. They battle the band of bandits and defeat them, finding a letter from a nearby town instructing the bandits to steal for them. The players head for this town with ample opportunity to have an extended rest.
The party is solving a mystery. A classic who-done-it with many characters and sub-plots but only one murderer, whom they finally confront and fight. If the murderer had an army in his command, it would be incongruous with the rest of the plot.
Ignoring the fact that both of the examples could have other battles shoe-horned into them, that's not always the ideal solution. My players want to explore a world, not kill everything in it.
In these situations it would be best to be able to create a single battle with the difficulty of a series of battles. However, I haven't found anything in the DMG or DMG2 that deals with this problem.
What I am looking for here is a practiced formula (not a guess) that consistently produces very hard battles. What would be a good formula I might use given the party's level that would enhance it to be equivalent to your basic dungeon of the party's level? What I am looking for here is a practiced formula (not a guess) that consistently produces very hard battles, that don't TPK, based on the party level that can scale from level 1 to 30. The point is not to add Skill Challenges for extra XP, but to make very challenging Combat Encounters that yield large XP while still being enjoyable. The part I'm having trouble quantifying is the lack of short rests, the lack of milestone action points and such. I need the battle to be hard, get them to the brink, but not be so hard as to run a risk of TPK. And ideally be balanced enough that I'd only sometimes need to have the enemy 'call for backup.'