The embroidery class shows there is a big interest in embroidery on this site.
I am figuring out how to make more different types of flowers than just the ones discussed in the online class and I am sure more people would enjoy a new, beginners level challenge.
All stitches I use are part of the embroidery class, so if something is not completely clear, you can check there.

There are a lot of dandelion embroideries out there, all of them are those fluff balls people use to make a wish.
The only embroidery example I found from yellow dandelions was by etsy seller KasiaJ

My flowers turned out a bit bigger and I did the leaves in a different way, but I still like them a lot.
For me this was just a practice piece, so I will only cover the embroidery itself.
You can find everything about how to finish an embroidery piece in the Instructables class, way better documented than I can.

Step 1: Tools and Materials

Tools

Embroidery hoop
Embroidery needle

Materials:

Embroidery thread(bright yellow, ligher yellow, 2 shades of green)
Fabric
Water erasable marker (or a pencil)

Step 2: Flower Outline

My local craftstore does not sell bright yellow embroidery thread and I need it in my actual piece, so excuse the color for my example flower.

I made a drawing of the direction of the stitches on KasiaJ's artpiece. Using different colors of washable fabric marker I drew the outer stitches, as well as the inner stitches that will be a lighter shade of yellow.

To get the desired thickness of the leaves we use all 6 strands.
Cover each of the outer stitch lines you just drew with a straight stitch.
Go from the outside to the inside and inside to outside to move between the lines.

IMPORTANT: Untwist your tread, untill there is no twist left, this will make your stitches look so much more like dandelion leaves.

The next step is to put straight stitches in between the first row, it will not look like a dandelion (see pic) but trust me, it will make the next step easier and prevent from any fabric showing. These stitches start halfway down your previous row, one in between every set of outer leaves and then one in between every set of those. All the way to the center.

Step 3: Filling In

I took a different color to illustrate the next step, but you should still use the same yellow.

Start with your tread next to one of the stitches from the outer circle and make it overlap the bottom of the stitch just a little bit. Do the same on the other side and for all other stitches on the outer row.
You will find that sometimes you need an extra straight stitch in between to keep fabric from showing and sometimes when leaves are closer together you only need a stitch on one side.
Follow your instinct.
I find laying the thread on top of the embroidery to see how the next stitch will relate to the previous ones very helpful.

Use slightly overlapping stitches on the next row as well. Then use a combination of some long stitches going all the way to the center and smaller stitches to fill up the gaps.
I did this with the bright yellow one, but only used small stitches on the darker flower, see the difference?

Take your lighter yellow color (also 6 strands) and stitch the lines from the center that we drew at the beginning.

Step 4: Base and Stem

Use a stem stitch for the stem.
I leaned this stitch for the flower sampler of the embroidery class. (check there if you want it explained with video)

Stitch a straight stitch on the line of you stem, about 7mm long.
Then bring your needle back to the front on the side of this stitch halfway down and make a stitch of the same length. Do this untill you reach the flower or the spot where the base starts.

Use flaired straight stitches from the end of the stem to the flower to form the base. It is ok if these overlap, nature is not always the exact same. Just make sure to put in some extra stitches to cover up any visible fabric, from the flower down in between the other stitches.

Step 5: Leaves

For the leaves I use a darker green, in a closed fly stitch.
Dandelion leaves are a bit jagged, so I drew the shape I want to end up with on my fabric with pencil.

Bring your needle up at the end of the leaf, and make a small stitch down the centerline of the leaf, about 1/4 inch.
Then, bring the needle back up to the right side of the middle stitch on the pattern line.

Go down on the left of the center stitch on the pattern line, angle the needle back to the center line and bring it up just below your previous stitch.
Take your needle over the working thread, pull it tight and anchor the stitch to keep the loop of floss from the two side stitches held down.
Repeat this on the line you just drew

If you are a n00b like me, it is easy to first stitch the big pointy stitch in place and then finish the last small stitches, that came before it.

I tried giving one leave a different color vine for fun (this is a test piece, I might as well test multiple things) but it was a lot of hassle.