Here's a fun photo and shows one of the benefits of using a glue block.
I can move my tool rest right around the blank and work on the
back of the turning.
You can see that I'm now cutting the outside edge to put a nice flair
on the piece. This will make it look lighter and helps to emphasize
the bead at the top edge. Be careful with your cuts as they can
grab more from this side.
Also notice the pencil mark that I've made on the back. This is going
to be the foot.
My top bead and bottom edge is now formed. You can see the nice sloping
angle of the side of the platter.

In this picture you can see that I've cut the beginnings of the foot.
I used a parting tool and cut the outside of the foot to the
full depth (~1/4"). Then I used the bowl gouge to smooth this
new depth into the outside curve.
Then I started cutting inside the foot. Since I have access to this
space, I'm just lightening up the piece.
There are lots of ways to reverse your platter. In this picture, I'm
taking advantage of the Oneway live center. There is an adapter
that can screw onto the live center and allows you to attach
your chuck to the live center, isn't that cool!!!
By going to all this trouble and mounting the blank this way, my platter
will be supported as I cut off the glue block.
If you don't have a cole plate, you could use a jamb chuck with your
tailstock providing support. Cut away everything that you can
with your turning tools and then carve away the stem left holding
the tailstock with carving tools (either hand tools or power
carvers).

Here is the finished foot. I've cut way up into the space that supports
the tile onto the top of the platter. This is excess wood and
just adds weight. By removing this waste, I can lighten up the
piece. It's already going to be heavy enough.

Here is the finished piece with the tile set into the recess. I will
now able a finish to the piece. I like using 6 to 8 coats of
Tung Oil finish. It's very strong and easy to apply. The tile
will then be mounted using a bead of silicone glue available
at the local hardware store.
Here are a couple of examples of finished pieces
15" Mahogany in the style of this tutorial

12" Maple with minimal recess, green marble tile and strong beads