Yeah, I know that is so crazy. I can honestly say that I don't think I have ever cleaned the oven in the 4 years we have had our oven. Shortly after us moving here, our oven went out. It went out on Easter weekend and we ended up having to cook dinner in our oven/microwave in one. Luckily it did a great job. So if you ever have an emergency with your oven and you get stuck without one.....the microwave with the oven rack/broiler at the top works beautifully.
Sprinkle baking soda on your mess and spray with vinegar. When you spray the vinegar onto the baking soda it will fizzle up. I did not use a specific amount, just enough to coat my oven.
* Don't spray the heating bar, because it will cause a white and yellow residue to splatter off it onto the oven walls when it heats up.
I actually scrubbed and repeated because it was so disgusting and dirty. So it actually took all night and then the next day to clean. I have seen where other people have had those magically over night and scrub miracles, but I was not so fortunate. I really have no clue why I have never cleaned the oven before. I really didn't pay attention to how yucky it was. I mean from the beginning to the end it was a major difference. I know you can't see to well on the difference I got out of the oven racks but it worked. I mean it is not perfect, but the rest really wouldn't come out. When I was scrubbing...I used the potato smasher to hold up the heating glow bar thing(sorry I have no clue what it is called).
After the fact, I covered the bottom with foil to catch any further messes. I also make sure that I am putting any casserole dish or other dishes placed in the oven on a cookie sheet or jelly roll pan to make sure nothing is spilling out into the oven again. It is said that the food tastes better when you bake it if your oven is clean. That is the main reason that I went to take a look at it and discovered that mess. My oven is still clean and I can promise you it will never look the way it did again. For the record....the food does seem tastier. I am not sure if it is because the oven is clean or the fact I KNOW it is clean that makes it taste better.