Making good hot chocolate is a delicate balance of ingredients and though many may be added what really matters is who you have it with.

1: Baby it's cold outside:

The first time he makes her hot chocolate, it's an instant packet after visiting him in Central City. Because they had a run in with Captain Cold. He heats the water in a Flash museum mug and stirs it with a fork. The chocolate at the bottom of the mug still tastes like raw coco.

2: Late night Lactate:

The second time, is when insomnia hits at the base. Still a little too wired from the mission and finishing homework she heads to the kitchen and runs into Wally's 2:45 AM snack. He heats them both up milk in a pan and stirs in adding chocolate, honey, and cinnamon to taste.
She could barely keep her eyes open after discussing the lack of flesh eating unicorns in the horror genre. Needless to say after the really strange (no she doesn't like him.) dream she had breakfast was…awkward.

3: Mad Science!:

Putting the marshmallows in liquid nitrogen makes lukewarm chocolate Kid Fail.

4: Welp:

Never dump an entire tin of Altoids in a mug of hot chocolate. Never consume it on a dare.

5: Technicalities:

He finally learned how to make her hot chocolate perfect, through careful observation: six mini marshmallows, one square of dark chocolate added after and stirred with a candy cane.
Of course she learned his too, they pretended they were going to drink it, only to have the other steal it and then retaliate taking the other's original mug, thus both kept up the facade of not being so into each other, and both obtaining their proper drinks.

+1. Merry Christmas Baby:

It was Christmas Eve in the frigid condo. She had set the pan on the stove for her vigil two mugs waiting, supplies on the counter and wrapped up in a warm fluffy blanket. Artemis took a deep breath the scent of coca overpowering the laundry detergent on the blanket and that background smell of their condo.

She already had consumed one impatiently made in the microwave. As she nearly drifted off to sleep a flash of thought crossed her mind: He missed the check-in.

Artemis 28 Calling Watchtower. Please send me the last known coordinates of Flash 27.

Her heart pounded as the car ramped up the drifts, heater on full blast. Thermal blankets in the back seats.

"Hey Baywatch wake up! Wake up please! You know a good ninja boyfriend doesn't pass out in the snow, on Christmas Eve, make his verypregnant wife come to the rescue, and then die on her…" The last part came out as a pleading half-sob.

She got him in the back seat and wrapped him in the blankets and used the seat-belts to strap him in tightly. She ignored the tears adhered to her face as she drove carefully, so not to dislodge him from his spot or get stuck in a drift but still racing frantically.

"I swear to god Baywatch if you die on me…I'll let Jade pick what you get reincarnated as."

Nearest transporter, nearest transporter… is back at our place.

She dragged his unconscious body past the counter knocking over the mugs the contents mixed on the floor as the shards co-mingled.

The holiday party they were late for stopped as they arrived.

…You'd think as heroes that they wouldn't freeze up that they'd be prepared to respond.

Artemis took a deep breath and shouted,"I need a stretcher, and someone prepare treatments for hypothermia and frostbite! Stat!"

A couple hours later in the monitor womb, (the only place he hadn't plastered holiday decorations thanks to a well timed bat glare.) the news arrived that he was conscious. She snagged a couple paper cups with lukewarm chocolate the marshmallows long dissolved into foam and took the long walk to the med-bay.

"You!"

"Merry Christmas Beautiful."

Needless to say she spilled her third and fourth cup of hot chocolate to night on his head and lap respectively. She then proceeded to get into the bed with him.

She ducked as an arrow affixed itself to the wall above their heads. Recognizing the fletching she immediately turned to storm after the culprit.

"Lian!"

Only to have herself be restrained by Wally. She glared at him and he pointed with his free hand. As she looked up she was suddenly pulled down by both hands on top of him.

"Mistletoe."

The chocolate had dripped down from his hair to his face.

"Artemis, Could you please get up?"

"Nope."
She snuggled closer ignoring the sensation of spilled hot chocolate being soaked up by her clothes.

"I'm keeping you right here warm in my arms until you decide to use that brain of yours for more than getting yourself stuck in endothermic reactions."

"Hey…"

Grey eyes met green with a teasing light.

"It would take forever to train someone else in how I like my hot chocolate."

"Six marshmallows, one piece of dark chocolate, stirred by a candy cane and not so hot as to burn."

"Well that's one way I like it."

She licked a drop running down his cheek and initiated the kiss this time.

Wally and decorations comment referencing Lavander Gaia's: Nothing in Moderation

Here's the prompt:
Five times Wally made Artemis hot chocolate, and the one time he didn't.

Roll with it, just make it fluffy and adorable.

Bonus: If you throw in that Art likes six little marshmallows or two big ones.
I wish I could link to the other fill but I can't.