See ECMA 334 §17.4.5.1:
17.4.5.1 Static field initialization
The static field variable initializers
of a class declaration correspond to a
sequence of assignments that are
executed in the textual order in which
they appear in the class declaration.
If a static constructor (§17.11)
exists in the class, execution of the
static field initializers occurs
immediately prior to executing that
static constructor. Otherwise, the
static field initializers are executed
at an implementation-dependent time
prior to the first use of a static
field of that class
Specifically: “execution of the static field initializers occurs immediately prior to executing that static constructor”.
Your static MyClass aVar must be initialized before your static constructor executes (or, at least, it must appear that way). Without that static member, the static constructor should be called before any non-static constructors.
If you still want a MyClass singleton, you can put it in a container class and refer to it using that, e.g.:
public static class MyClassSingleton
{
public static MyClass aVar = new MyClass();
}