Why is my peppermint slice base so crumbly!

I have a recipe for peppermint slice and the base is nice but very crumbly, this is it.
2/3 cup self raising flour,
1/4 cup cocoa,
1/2 coconut,
1/2 sugar,
140 g melted butter,
1 egg
You just mix altogether and then bake for 15 minutes.

Any suggestions to make it less crumbly would be welcome or a recipe that you may use yourself. I have tried other coconut type bases but am finding them a little dry. Thanks.

addmorebuttertocombine,140gsdoesseemlittleforallthosedryingreds

I'm not sure that would be the answer as the mix is not at all dry and when I pat it into the tray all the oil rises to the top. Thanks.

try eliminating the coconut, but you may need to increase the flour, if the mix looks sticky.
searching for my old recipe will post for you.

Sorry realised the recipe I just deleted had even more coconut in. Try this uncooked one from the NZWW cook book:
CHOCOLATE PEPPERMINT SQUARE
125gms butter
3/4cup sugar
1 TBSP cocoa
1 egg
1/2 tsp peppermint essence
250gms crushed wine biscuits
Icing:
1 1/2 cups icing sugar
1 TBSP custard powder
1 tsp melted butter
few drops peppermint essence.
METHOD:
In a small saucepan heat the butter, sugar and cocoa until melted, then add the egg and beat well with a rotary beater. Cook for a further minute, stirring all the time. Add the essence and crushed biscuits and mix well. Turn into an 8inch by 12inch sponge roll tin and leave to set.
When base has set ice thinly and leave overnight to set completely.
TO MAKE ICING:
Sieve the icing sugar and custard powder together , and stir in the melted butter. Add the flavouring to suit own taste, and mix the icing to spreading consistency with a few drops of water if necessary. After this is set:
A CHOCOLATE TOPPING made from 200gms melted choc chips and 60gms kremelta can be added over this if desired, but is not essential.

Thanks Kinna, using a crushed biscuit base might be a good option.