Here`s how I made my sons baby feet for gift giving. Hope someone out there can use this.
I had a heck of a time figuring out what to use as a mould. I thought of clay, but that`s too hard. I tried foam clay, but it puffed and lost some definition when dried. Then brainwave: salt dough. Duh! it`s cheap and the ingredients I already had. Let`s get started.

Step 1: Gather and Prep

Salt dough:
1 half cup flour
1 half cup salt
1 quater cup warm water

medium size bowl
aluminum foil
bakeware
cornstarch
whisk
spoon
disposable container
plaster powder
baby lotion
2 grades of sand paper- 1 coarse and 1 smooth.
rotary tool with sanding attachment is supremely helpful.
scissors

Use aluminum foil to line the bakeware which should be large enough to fit the subjects feet in comfortably. Measure out dough ingredients.
Note: in order to rescue tools from plastered existence have a container of water handy during the plastering process. Just pop them in when you are done until you can get back to them to be washed.

Step 2: Make Salt Dough

In the medium sized bowl sift together flour and salt. Mix together while `fluffing`the mixture. I can`t really explain it, just sort of fluff it while stirring. Slowly add the water while stirring until it looks crumbly. Knead with your hands until it forms a cohesive ball of dough.

Step 3: Make an Impression

Roll salt dough out inside aluminum lined bakeware to about 1 to 1 and a half inch thickness. Choose your victim (subject) and lotion up the feet with the baby lotion. This next step may require another pair of hands (depending on the wriggle factor of your intended subject). Gently push feet into dough to make good impression. Make sure not to push all the way through to the bottom of the bakeware. Also try not to make impression too close to the edge as I had done. Bake at 200 degrees for 3 hours.

Step 4: Time to Get Plastered!

After the salt dough mould has cooled, sprinkle with cornstarch. I like to use a mini strainer to lightly sprinkle it. Next grab your disposable container and fill with 1 half cup warm water, maybe less as I made two sets of feet with mine. I know this is where I`m supposed to tell you to read the instructions on how to make the plaster. And I did. Then I ignored them and did it this way: Using the spoon I scooped out a little at a time and whisked it into the water slowly. Repeated until it became the consistency of thick cake batter. If you`ve never made cake then thick pancake batter. If you`ve never make pancakes then I can not help you. Poor you. :(
Pour plaster (or spoon it as I did) into moulds. It sets fast so don`t dawdle on this. If your mould has been made too close to the edge as mine was just use the aluminum foil to create a barrier around that edge. If you intend to mount plaster feet in frame or hang from wall I suggest you try to make the plaster as level and smooth as you can. Excellent! We are almost to the Really fun part. Now we wait. (That`s not the fun part)

Step 5: Back to the Grind

Now that your plaster is dry you can start sanding and sculpting.Gently lift plaster form from mould. If you are careful enough you can save the mould for another few uses. I used scissors to carefully clip off excess plaster around the feet. I also used a rotary tool with a sanding attachment to quickly take down the plaster into the basic foot form. I had to be careful not to take too much off as that sucker works fast. When you have the basic shape you want start off by using the coarser grade of sanding paper to sand the rough edges. Don`t worry too much about perfection. That`s what the smoother grade of sandpaper is for. Once done both feet now you`re ready for the fun part.

Step 6: Fun Time!

Now you can decorate your feet as you like. I used a base coat of plain white acrylic paint under pearlized white paint. Then added leafy greens and flowers. I intend to use a gloss protective spray. Don`t get too focused on using just paint. I used nail art decorations for the flowers. Imagine the possibilities! That`s it. Thanks for reading my first ever Instructable. Hope you new parents have fun with it and those of you who can use it for other things like rubber duckies (my next plaster project) or halloween decorations. :)