Template function inside template class

I have this code:

template <class T>
class MyClass {
	public:
    	template <class U>
		void foo() {
			U a;
			a.invoke();
		}
};

I want it in this form:

template <class T>
class MyClass {
	public:
    	template <class U>
		void foo();
};

template <class T> /* ????? */
void MyClass<T>::foo() {
    U a;
    a.invoke();
}

How I can to do this? What is the right syntax?

Write this:

template <class T>
template <class U>
void MyClass<T>::foo() { /* ... */ }