I was headcanoning around with trufflemores and suddenly this happened, because I have a mighty need for something like this to happen in canon. Happy early Thanksgiving, fellow Americans!
Blaine was curled around Kurt and dreaming of them having a quiet picnic in Central Park one day when a rhythmic knocking woke him up. Shifting closer to Kurt and keeping his eyes shut, he slurred "Who's there?" as though it was one word.
"It's almost noon, boys, if you don't get up soon we'll eat Thanksgiving dinner without you," he heard Burt say, chuckling. "C'mon, up and at 'em."
"No, Dad, give us five more minutes," Blaine groaned, burying his face into the back of Kurt's neck and not realizing what he had said. Kurt snuffled a bit but continued to sleep; he always slept harder than Blaine.
If Blaine had been looking at Burt, he would've seen the man's eyes soften and a pleased smile erupt on his face. As it was, all he felt was Burt coming up to rub his ankle and say "Okay, kiddo, five more minutes."
Blaine gave a pleased grunt and fell back to sleep almost instantly. He was properly woken up half an hour later by a chipper Kurt giving him a smacking kiss on the forehead, his earlier conversation with Burt only a vague recollection in the back of his mind.
A few hours later, he, Kurt, Burt, and Carole were all sitting around the dining room table for Thanksgiving dinner, sharing what they were thankful for.
"I'm thankful that I can have dinner with my lovely fiance and his family rather than sit through another Anderson Family Bragfest," Blaine said, somewhat bashfully from his spot on the right side of the table. Kurt was across from him and smiling, while Burt and Carole had seats on the short sides, Burt's angled so he could still see the game while talking with everyone.
Carole leaned over and gave Blaine a quick hug around the shoulders before saying "You know you're always welcome here, Blaine." She waved off his thanks and continued, "Anyways, I'm thankful for...life going on, I guess." Her voice trailed off as she stared into the middle distance, obviously thinking of Finn. "I'm thankful that it's slowly getting easier."
Kurt continued the hug-your-neighbor train and leaned over to squeeze his stepmother tight. "I'm thankful that Blaine and I can be home for the holiday," he said after releasing her, beaming a smile to the whole table. "Also for Carole's famous cinnamon pumpkin pie!" Kurt rubbed his stomach in anticipation.
Burt gave Kurt a brief one-armed hug and rubbed his back a little. "Well, I am thankful for my amazing wife and sons," he said. "I'm glad we can all be together for a little while."
Blaine and Kurt stared at each other in confusion for a minute before Kurt turned to look back at his father. "Dad, what do you mean 'sons'?" he asked. "Carole's not pregnant, right?"
"No, buddy, Carole's not pregnant. Someone," he said with a pointed glance at Blaine, "might have called me Dad this morning."
Blaine felt his cheeks heat up and immediately focused his eyes on the pattern on his dinner plate. "I'm so sorry, Burt. I was half-asleep and-" Burt cut him off before he could keep making excuses.
"Did you hear me saying I wasn't okay with it, kiddo?" he asked, smiling. "You've been around for years and you're marrying Kurt, I think that gives you the right to call me Dad."
"Really?" Blaine turned his head to stare Burt in the eyes, a little flabbergasted. "That's- I don't know what to say. Uh, thanks...Dad."
A small sob from Burt's left broke into the moment. Blaine faced Kurt to see a couple of tears trickling down his face along with a luminescent, toothy smile. "I'm sorry. I just- you know you two are the two most important men in my life, right? Well, along with Stephen Sondheim," he joked, wiping his face. "I'm so happy you two get along."
Blaine looked back at Burt, smiling conspiratorially. Burt gave him a matching smile, letting Blaine know they were on the same page. In unison, they grabbed for Kurt, Burt pulling him towards himself as Blaine leaped out of his chair to come around and snuggle into Kurt from behind.
"What – you guys – ack!" Kurt spluttered out, giggling a little bit at the antics of his father and fiance. "You two are ridiculous and no longer my favorites. Carole's taken that position over," he tried to say haughtily, but the giggles he was stifling ruined the effect.
"Yeah, okay, buddy, I believe you," Burt said with a laugh, releasing his son. "How about you, Blaine?"
"I'm not so sure," Blaine replied, still wrapped around Kurt's waist but adjusting so they could both stand up straight. "I think I'm still his favorite," he continued on with a smile and his head hooked over Kurt's left shoulder. He could see Carole smiling back at him out of his peripheral vision.
"In your dreams, Anderson," Kurt said, playfully trying to fight his way out of Blaine's grip. "Now let me go, the food's getting cold!"
"What's the magic word, baby?" Blaine asked, tightening his grip slightly.
"Please?" Kurt said, stopping his fight to turn in Blaine's arms so he could see the pout on Kurt's face.
"Not quite, but I'll let you have it. I was looking for 'Of course you're my favorite, B,'" said Blaine, letting go of Kurt and starting to walk back to his seat.
"I cannot tell a lie, B," Kurt laughed as he sat back down.
"Shut up and eat your pie," Blaine said with a fake huff, taking his own seat.
"That's okay, kiddo, you know you're my favorite son," Burt stage-whispered to Blaine with a wink.
"Hey!" Kurt yelled, giving his father a joking version of his death glare.
"Boys, can this argument wait? I'm starving," Carole broke in, reaching for the closest serving platter to start loading her plate.
"That's fine, but don't you dare think this is over, Dad," Kurt acquiesced, starting to fill his own plate.
"Wouldn't dream of it, son," Burt responded, and they all began to eat. Kurt and Blaine finished first, and excused themselves to the living room to take a nap.
"I can't believe you've replaced me as my dad's favorite," Kurt said, grumbling a little but with no real heat behind it.
"What can I say, it's the Anderson charm," Blaine responded, shrugging a little. "Now c'mon, let's nap before Dad makes us do the dishes later." He slowly began to drift off, but had to get out one last thought before succumbing entirely to sleep.
"Hey, Kurt?"
"Yeah, B?"
"This really has been the best Thanksgiving ever."
"Agreed."
And with that, Blaine and Kurt settled down for a truly excellent almost-winter's nap.