"I have to admit Buttercup's mother-in-law makes Apple Pie way better then the chefs at Canterlot." Celestia said.

"It's all thanks to Mrs. Apple Smith's secret ingredient." Buttercup said. "Something she says is top secret information." She added.

"Well I suppose it is more homemade." Luna said.

"Well up next is Sugarcube Corner where our friend, Chiffon Swirls works." Spitfire said. "Chiffon Swirls also happens to be in charge of the party that'll happen after the Sun Celebration event." She added.

"I'd be happy to attend it." Celestia said. The foursome entered to see two more earth ponies working.

"Hiya Chiffon Swirls." Luna said.

"Oh Luna, it's good to see you. Whose your new friend?" Chiffon Swirls asked.

"This is my sister, Celestia." Luna said.

"It's nice to meet you, Swirls. You don't mind if I just call you Swirls do you?" Celestia asked.

"No not at all." Chiffon Swirls said. The stallion came over.

"Is there something your here for?" He asked.

"Hi Mr. Carrot Cake." Buttercup said. "Celestia here is just checking on preparations for the Sun Celebration event." She added.

"WHOOPS!" Chiffon Swirls accidently tripped as she was carrying four cupcakes, which got all over Celestia and Celestia only.

"...Okay how'd that miss us?" Spitfire asked.

"My apologies sir..." Chiffon Swirls said. Everyone noticed she slipped on something of Carrot Cake’s.

"Oh there's my wallet. This is my fault, Chiffon Swirls; I must have dropped it while we were busy making sure things would be ready for the after-party later." Carrot Cake said. "...Come to think of it, the place could use some cleaning up. Why don't you go out and let me get things cleaned up back here? I'm giving you permission to go to the Sun Celebration event with your friends. Oh and...find somewhere to get Celestia cleaned up would you?" He asked.

"Yes sir." Chiffon swirls said.

"Wow, your boss is pretty nice to you." Celestia said.

"He's the best boss I could ask for." Chiffon Swirls said. "Though one day, I'd like to be more then just his employee..." Chiffron Swirls said under her breath.

"Hmm? What was that?" Celestia asked.

"Oh um...just me talking to myself. Say, let's go over to Cookie Crumbles, she'll get you all washed up in a hurry." Chiffon Swirls said.

The five mares were now at Town Hall, where a lone Unicorn Mare stood.

She finished setting up the decorations before turning towards her friends and screaming at the sight of Celestia still covered in Cupcake batter.

"Yeah you can tell where we last were..." Spitfire said.

"Dear, we should get you cleaned up at once!" The mare said. A bit later, Celestia was in a bathtub, enjoying some time there. "So, your Luna's sister. It's an honor to meet you. I'm Cookie Crumbles." Cookie Crumbles said.

"And I am Celestia. It's a pleasure to meet you too." Celestia said.

"So your all done with the decorations huh? That's good. So, what do you say we all head to where Celestia is staying and have ourselves some bonding time. You know, to solidify our friendship with Luna's sister." Chiffon Swirls said.

"That would be nice. Ah'm sure Mrs. Apple Smith would understand." Buttercup said.

"You know she will. Like she said, it's not every day Princess Twilight's own student comes down to visit a place like this." Spitfire noted.

"You said it Spitfire." Luna said.

"Count me in. I'm all done with stuff so, when your ready, Celestia." Cookie Crumbles said. Celestia smiled.

The Unicorn Mare that was the student of Princess Twilight had no idea why the ruler of Equestria wanted her to make friends rather then worry about an obviously evil entity. But Celestia had no reason to question her mentor. Besides, Celestia figured it could be a back-up plan for Celestia to have help in case the Alicorn Princess could not stop Shining Flare.

...

If only she would've realized the real reason why, then maybe she'd know why her mentor was so instant on the Unicorn making friends.

For now, blissfully unaware of the battle to come, the six mares enjoyed plenty of games together, each one regalling Celestia with what they each knew about the five who were known to have helped Princess Twilight Sparkle form the High Coincil. To which, Celestia was all too happy to give her take on the same five mares.

Those mares being Pinkie Pie, Applejack, Rainbow Dash, Rarity, and Fluttershy.

Author's Note

According the official MLP:FiM wiki, Mrs. Cup Cake's maiden name is Chiffon Swirls. While she and Carrot Cake are not yet married in this timeline, it is being heavily implied that she's in love with her boss. For those expecting Hondo Flanks to be part of this timeline, hate to say it but Hondo Flanks is being saved for something much later on.
To the keen observers who have been paying attention might have noticed that Celestia encountered Spitfire, Luna, Pear Butter AKA Buttercup, Chiffon Swirls, and Cookie Crumbles in that order.
Conversely, in the original timeline, Twilight had met Pinkie Pie, Applejack, Rainbow Dash, Rarity, and Fluttershy in that order. Before anyone tries to correct me on this order, while Pinkie Pie was named much later in the first half of the series premier of MLP:FiM, she was technically the first one Twilight came across of the elements of harmony.
For this story, I decided to remix the order in a way that would still make sense. Thus, encountering Spitfire first was key so Celestia could then reunite with her sister.
FYI, the title is meant to be a pun on the phrase "Milk & Cookies" but changed to fit the two characters being properly introduced here.