To do the Butterfly Crunches, start seated and let your knees fall open as you bring the bottom of your feet together. With the bottoms of your feet together, bring your heels in toward your body. Exactly how close you bring them in will be dependent on your flexibility and hip mobility.
Then lie back with your legs in the Butterfly Stretch. Place your hands behind your head with your elbows relaxed out wide. There should be a space between your chin and your chest as you relax your head in your hands.
Then crunch up, pressing your low back into the ground. Lift your shoulder blades up off the ground while keeping the space between your chin and your chest. Do not tug on your head with your hands to lift up higher.
Crunch up and then lower back down. Each time you crunch up, press your low back into the ground.
As you crunch, make sure that you are pressing the bottoms of your feet together to help keep everything engaged.