I have tried cooking beef (mostly London broil type) so many times... And it never comes out tender! I've tried different methods... Temperatures... Everything! It always comes out tough and chewy. I thought maybe it was the type of meat I was using, but I had my mother cook the same exact type of beef at her house... & it came out perfectly. I asked her how & she said she just does it! And she sautéed it on the stove... I did the same thing a week later, & it turned out bad. What am I possibly doing wrong?