Even tho I am new to Blender, I have tried many techniques posted on stack. However, I can't find a way to make this shape with a solid element (with faces).
- Subdivide a Plane (W > Subdivide) as much as you need, keep in mind to have vertex in the center of a Plane. So you will need odd number.
- Select vertex in the center.
- Turn on Proportional Editing (you can switch trough different falloffs to get different results).
- Scale down (S) and increase Proportional Editing influence size - MouseWheel.