Does anyone know what that thing she's holding is? I thought it was a giant sunflower seed from the thumbnail, but the stem means it's not.

Looks like some kind of gourd or a pumpkin.

Commentary from Mokku's blog
http://mocksunflower.blog53.fc2.com/blog-entry-16.html

Title: バレンタイン
ちょっと遅れたけどゆうかりんの手作りチョコ。
さすがゆうかりん、カカオから手作りだよ！

…チョコ…？

Title: Valentine
Happy Day After Valentine's Day! This is Yuukarin's hand-made chocolate.
As expected of Yuukarin, she created it from cacao beans!

......chocolate?

henmere said:
explanation

ah, that's soo much better. Thank you Henmere

*smacks forehead for not thinking of reading the source page*

Thank you for that. Tagged as cacao fruit.