Multiply elements of a matrix along its third dimension

For programming in MATLAB, how can I write a function that will take a stack of matrices in a variable (let's say M) and multiply them together and return in answer in an output argument.

It would be preferred to put M as an input argument of the function. And it might be easier to use for loops to multiply each layer to the previous.

Help would be greatly appreciated, thank you!

To help start:

M(:,:,1)=[1 2,3 4]; %first layer
M(:,:,2)=[5 6,7 8]; %second layer

That function is called prod. Try this

newM = prod(M,3);