It's a simple process to make a card base from any die. First cut a piece of cardstock at least twice as long as the die you are using and score in the center.
Fold. Place the fold just inside the cutting line of the die, as shown here.
This is such a fun and easy way to make a unique card shape. If you haven't already tried this technique I hope you will. You can use a multitude of die shapes for this idea. Here is another way to use this technique on a card I did some time ago.
My Creative Time, Capture Frame die
My Creative Time, Vintage Label and banner die set
My Creative Time, Round Speech Bubble die
My Creative Time, Wow, So Many Candles stamp set
My Creative Time, Chocolate Greetings stamps
My Mind's Eye, Kraft Funday Happy Days 6x6 paper pad
Twine, button, bling, acetate for window