Need advice with error - while defining a function outside a template class

Question

Here is this class:

template<typename T>
class TestClass
{
private:
    struct element
    {
        T data;
        element* ptr;

        explicit element(T val) : data(val), ptr (nullptr) {}
    };
    element entity;

public:
    T foo(int);
    void fee(const TestClass&);
    element* faa(T, bool order = true);

    explicit TestClass(T p1);
    ~TestClass() {}
};

while I tried defining the following function outside the class as:

template<typename T>
TestClass<T>::element* TestClass<T>::faa(T val, bool order)
{
    //blah blah blah
}

I got the following error: (compiling on this site)

main.cpp:36:1: error: need ‘typename’ before ‘TestClass::element’ because ‘TestClass’ is a dependent scope
   36 | TestClass<T>::element* TestClass<T>::faa(T val, bool order)
      | ^~~~~~~~~~~~
      | typename 

I tried searching on stack overflow - got THIS page. But I am still not understanding where is my error. Kindly advice.