I am a fairly new baker and I need some suggestions. I started when my son was diagnosed with a peanut allergy a couple of years ago and have only made cakes for us and some family members. 

I am making cupcakes for my nephew's 2nd birthday party in July and need a replacement for butter in the cupcakes as well as the buttercream. It needs to be peanut/tree nut, coconut, soy, dairy, banana & avacado free. (The peanut/tree but & coconut are allergies, the rest are intolerances) Any ideas?

you'd have to track down what the modified food starch is in "just mayo" but you can get a great chocolate cake with it -- and maybe other kinds just never tried any other --

http://www.hamptoncreek.com/just-mayo/recipes/chocolate

and maybe you can rig up some icing with it?

p.s. in some locations they sell cookie dough too

I never thought of mayo. I've never heard of 'just mayo'. (I'm in Canada), but I will have a look at my mayo and maybe give that a try. 

just mayo is a special product -- it is eggless and tastes and seems just like regular mayo -- comes out of san fransisco -- 

Geez, why not jusr serve rice cakes with a side of water!

Use a recipe which uses oil, you can use canola oil instead of soy/peanut oil. As far as the butter, you need something to replace the fat, not sure what you would use. Maybe there are other types of dessert toppings that don't have these kinds of allergens in them besides regular icing? Also, Earth balance makes a soy free spread (and baking sticks), not sure if you can use margarine in icing, I seem to remember someone saying they did it, but I think they also used coconut cream.

http://earthbalancenatural.com/product/soy-free-buttery-spread/#

Are eggs totally out of the picture also?  They're not considered dairy, but with everything else going on, you may have to look for vegan recipes.  (FWIW, I have baked some vegan cookies whilst at work waaaay back when, and they were *extremely* dry.  They used a water and ground flaxseed combo to replace the eggs, and I have no recipe.  Anyhoo...)

If eggs are ok, maybe chiffon or angel food recipes?  Those use the air whipped into the eggs to help with the rise, and rely on vegetable oil for the fat, rather than butter.  I don't know how well they work with cupcakes, as I've never tried that.

bakerblackcat -- great idea -- angel food is fat free -- all meringue with a little flour -- great idea if eggs are allowed -- and i have made it in various sizes -- not sure how it would play as a cupcake though -- i mean it would bake ok just don't know how it would emerge from the wrapper -- it would stick and the more you pull the more it would squish -- idk

but as cake -- perfect

Yeah, I'd consider baking mini-cakes (3" and smaller) and topping them with some sort of non-dairy whipped topping.  Angel food cake is so light & yummy, I don't know that I'd want to be limited to just a cupcake!  Mez1225, I've no idea what non-dairy toppings are available in Canada, but another alternative would be to just melt some good quality chocolate and drizzle that on top. Hope that helps!

strawberries

Thanks for the replies everyone! Yup, eggs are allowed and mini cakes could be really cute. I'll see if she's up for angelfood

I'll double check the vegetable oil, but most chocolate bars are off the table due to milk and nut cross contamination 

Another option, carrot cake cupcakes with seven minute frosting.  Frosting is made with egg whites and has none of the ingredients on your "no" list.  If you want recipes, just post.  I am in Canada too.

I would love the Frosting recipe!

I do angel food cuppies all the time... Make sure you use a cupcake liner that is foil... The paper sticks to the cake...

SEVEN MINUTE FROSTING

Equipment needed:  Double Boiler, Handheld Mixer

Ingredients:

2 cups white granulated sugar

3 egg whites

3 tablespoons light corn syrup

3 tablespoons cold water

1 teaspoon pure vanilla extract

Method:

Fill bottom of double boiler with boiling water and place over medium to high heat to keep water boiling.  Add all ingredients to top of double boiler and place on top of bottom double boiler pan. Beat with hand mixer on high for 7 minutes or until the mixture forms peaks when you raise the beaters.  Remove from heat and use immediately to frost cake or cupcakes.  Frosting has a marshmallow like texture.  Make sure your cakes are completely cooled before frosting. This frosting is best used the day before or day of the event as it has a shorter life than buttercream.

Further to the angel food cake cupcakes recommendations, my granddaughter doesn't like icing so we make angel food cake with raspberry or strawberries coulis.   Run a bag of fresh or frozen raspberries or strawberries in a food processor or blender until smooth.  Add stevia or sugar to taste.  Spoon over angel food cake.