Unfortunately, I don't have the tutorial laying around. But here it is in a nutshell --

You want an object to be your flame cloud -- I create something blobby in the metaballs modeler (although the explosion above was made from a simple sphere primitive). Then I apply the atomize deformer to the flame object -- settings of particle density 9.99, size of particles, 3.0 or so. Open this object in the vertex modeler with apply deformers on object ticked. Subdivide the thing (to make the outer edges round instead of faceted) and jump out of the vertex modeler. Duplicate the object and rotate it a tiny bit to get a bit of double bumping going on in the cloud shape. Apply a shader that has yellow and orange in the glow channels. Rotate the two cloud objects independently of each other to get some undulation going on, and scale the entire cloud down to very small, increasing the scale as the animation procedes. Add a particle fountain with no gravity and a and a maximum angle from up set at 180. Particle size should be small. The final touch is to use the aura filter.

Obviously, you'll want to play with the settings to your own taste.... The cool thing about the cloud object being a "real" 3D object is that as it expands it can consume the object that's blowing up.

I hope this helps!

• Dex