How do I prevent this cake from sinking?

[B'sgirl]

I'm throwing a friend of mine a baby shower in a couple of weeks. I despise most cakes, but this recipe was my grandmother's and I love it. Unfortunately I've never been able to make it without the middle sinking in. I want it to look nice for the party, so any tips you have would be much appreciated (I am about 3000ft above sea level):

1/2 c +2 tbsp shortening
1 3/4 c +1 tbsp sugar
2 large eggs
3 c flour
2 1/2 tsp baking powder
1 tsp salt
1 1/4 c milk
1 1/2 tsp vanilla

Cream shortening with sugar. Add eggs, Beat for one minute till fluffy. Mix powders together. Alternate powder mixture, milk and vanilla. Bake at 350 for 40 minutes.

 

[quicksilver]

The ingredients look okay, B's. I would add vanilla after adding eggs, adding each egg individually and mixing after each add.
Alternating flour mix with milk (liquid) is how I do most cake batters.
I'm by no means an expert though. And I don't bake at high altitude.
The only thing I can think of is:
1. don't open the door of oven before baking is done.
2. don't bang, slam, shake anything loudly while cake is baking.
(When we were kids and mom was baking, mom used to warn,
"don't slam anything, or the cake will fall!" And she was correct.
It did fall with loud slamming around)
Good luck. I hope wiser voices can be more exact for you.

 

[PieSusan]

My mom use to say don't let a cake cool in a draft.

I wonder if it also has to do with overbeating?

Or check the date on your baking powder to make sure that it is fresh and that no humidity got to it.