Having finally served/chased away the last customer, Pinkie wraps up cleaning and then drags your reluctant carcass down into her 'mad scientist retreat' right inside a huge cavity she dug right underneath Sugarcube Corner. before you ask, yes, she did check to see if it was safe from a construction standpoint before she hollowed out an enormous room underneath a building. Only a few moles sustained any injuries from the sudden fall.
With all the facilities set up ready to make the cake of Diablos, she sets up the exotic ingredients, brings out the recipe, and basically starts ordering you around the kitchen. However, it is in the middle of handling the 51R3N vanilla extract that she realises a small problem: according to the recipe, the butter must be added to the cake mixture while 'infusing the spirit of a true learned air. Mix until soft and fluffy'. Unfortunately, as there is no way for her to take knowledge and bottle it up (Twilight Sparkle might know, but she's not here as it is and it would be awkward to explain why you're breaking the law underneath a small confectionery shop) it falls to you to add the mixture. Apparently.
She therefore takes all 12 pints of vanilla extract, pours it all inside a measuring jug that goes all the way up to 12, and then taking out two smaller measuring jugs, she decides to set you a puzzle, hoping that your feelings can be transferred into the cake. Feelings are not an exact science you admit, but you suppose it isn't called the Magic of Friendship for nothing. Friendship can make rainbow-coloured laser beams. Anything is possible at this point.
Rolling your eyes at the puzzle in front of you, you immediately realise Pinkie gave you a classic. You had hoped for something harder, but the low props available and the immediate need to handle the N1GHT3AR3 300N butter 'with extreme care' has limited options. Nonetheless, you have your puzzle, now get cracking.
You have 12 pints of vanilla extract in a jug, enough to fill it all the way to the top. You also have a 8-pint jug and a 5-pint jug, and you need to separate the extract so that you have 6 pints of extract in two jugs each, by pouring the extract in the jugs one at a time. To make things harder, Pinkie has erased all markings on the jugs, so all you have to go on is the knowledge that you must pour until the jug is totally full to the brim.
Yawn. But nonetheless, it would be embarrassing to fail here, so get cracking, friend. Seperate the extract into two lots of 6-pints, and then pour in the batter.