Composite Type Argument Construction to a Function

create type my_type (my_test text, my_int integer);

create function my_function(my_type)
returns timestamp as
'begin
return (current_timestamp);
end;
'
language 'plpgsql';

In 7.3.5, we are trying to get around the 32 argument limit of the
functions WITHOUT re-compiling with a greater func_max_args (due to
operational reasons).

My question is - HOW do I construct the argument to
my_function(my_type) so that the function recognises that I am passing
into it composite data?

NB: The example function is just "junque" to test passing a composite
type to a function.

TIA