Start by cutting the cardstock paper to a size of 10 inches by 7 inches.

Fold the cardstock in half horizontally to create a card shape, making sure the crease is sharp.

For the pop-up cake mechanism, cut a piece of patterned paper measuring 6 inches by 3 inches.

Fold the patterned paper in half lengthwise and then unfold it to create a center crease.

On the center crease, measure and mark 1 inch from each end and cut up to the crease to create two tabs.

Fold the tabs inward to create a 'V' shape and then fold the entire piece of patterned paper in half again.

Apply glue or double-sided tape to the bottom of the 'V' shaped tabs and attach them to the inside of the card, just below the fold, ensuring they pop up when the card is opened.

Using the remaining patterned paper, cut out shapes of cake layers and decorations to glue onto the pop-up cake structure.

Write a birthday message on the inside of the card around the pop-up cake using a marker or pen.

Add any additional embellishments, like stickers or glitter, to enhance the design of your pop-up birthday cake card.

Allow any glue to dry completely before closing the card.