You left, making your way deeper into what Flowey called the "Core". You entered a darkened room when you heard a familiar, robotic voice talking on the phone with someone. You heard the phone hang up.
"Oh no." Flowey said
"OH YES! Welcome beauties, to the underground's premier cooking show!"
Magical, red, letters appeared reading, "Cooking with a Killer Robot"
"Pre-heat your ovens, because we've got a very special recipe for you today! We're going to be making a dust cake!"
"What's a dust cake?" you ask Flowey.
"That's when you take the dust of a deceased monster and make a cake out of it." Flowey scrunched his face up. "It's Sans's favorite food. Well, next to mustard."
"Everything comes back to Sans, doesn't it?" you ask Flowey, but before you got an answer back, Mettaton interrupted the two of you.
"Enough chit-chat! My lovely assistant here will gather the ingredients! Everyone give them a big hand!"
Streamers fell from the roof of the cave. How, you weren't sure.
"We'll need dust, milk, and eggs. Go for it, sweetheart!"
You didn't want anything to do with the dust of monsters, but you went and got it for Mettaton. You didn't really see any other option.
"Great job! Just put them in the middle of this counter!"
You put everything on the counter and watched Mettaton to see what he would do next.
"Perfect! Great job, beautiful! We've got all of the ingredients we need to bake the cake! Milk, dust, eggs. Oh my! Wait a magnificent moment! How could I forget? For this particular recipe, we need one more thing! We're missing the mo-"
"It's human flesh, isn't it?" Flowey sighed. Mettaton looked a little taken aback by Flowey's realization, but continued never the less. His right arm morphed into a chainsaw and started advanced towards you.
Flowey screamed, "Wait a second! Couldn't you make a substitution the recipe?"
"A substitution? You mean, use a different, non-human ingredient? …Why?"
You had to think fast.
"Um… what if someones… vegan?" you ask
"…Vegan. That's… a TERRIBLE idea, human and flower. I don't know how it works where you come from, but no one down here is vegan. That would require caring about how others feel, and everyone knows down here it's every monster for themselves!"
It looked like you didn't think fast enough. You were in a panic and tried swinging your knife through Mettaton's microphone. Maybe you could knock the microphone out of his hands and when Mettaton tried to pick it up, you could run away.
The knife cut straight though Mettaton's mic. Mettaton stared at the remainder of his mic.
"Wow. Sans wasn't joking around when he gave you that knife," Flowey said.
There was a moment of silence.
"Well, toodles," Mettaton said.