I used boiled sweetened condensed for my caramel cake filling. Make sure the unopened can is totally covered in water, and simmer about 4 hours. Keep it covered in water, or it can explode! You have to watch it! I've heard you can dump it in a pan and simmer it that way, but have never tried it.
Forgot to say...Let it COOL totally before you try to open the can!!!
People LOVE the fluffy caramel filling I use. I stumbled across the WBH buttercream at CakeCentral. It's a "not so sweet uttercream". Since the Oreo filling recipe from CC didn't really cut it for me, I decided to use this fluffy buttercream and crush Oreos into it. People LOVED IT! From there I started adding in everything - peanut butter, caramel ice cream topping, dulce de leche, etc. It is the BEST to work with. It's not sweet, so the flavor of the add-in's really pop.
I add caramel ice cream topping to this (like 1/4 cup caramel to 1 1/4 cup frosting, but you can go with whatever taste you like).
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Whimsical Bake House Buttercream
In Mixer bowl, stir together:
6 Cups Confectioners' Sugar
1/8 teaspoon salt
1 teaspoon Vanilla Extract
Using whip attachment, add and whip on low speed:
1 cup boiling water (3/4 cup on hot days)
Whip until smooth and is cool.
Add and whip until smooth again:
2 3/4 cup Hi-Ratio or regular vegetable shortening
6 ounces (1 1/2 sticks) butter; slightly chilled and cut into 1" pieces
Turn up mixer to medium-high. Whip until double in volume and is light and fluffy. About 10-20 minutes. Recipe will almost fill a 5-quart mixer bowl when done.
Makes 9 1/2 cups
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You may have used this recipe before, but hopefully you'll try the new add-ins. You won't be disappointed. 
My husband is Filipino and loves these cakes from the Philippines. Check out the photo...it kind of reminds me of Ganache. Maybe if you let this one sit for a while and rewhip like ganache it could be a good filling. Otherwise I believe it goes over the cake like in the picture. and the recipe is from an international foods website.
http://www.cakecentral.com/cake-photo_27108.html
Carmel Frosting:
2 cups (475 ml) brown sugar
2 tbsp (30 ml) Butter
6 tbsp (90 ml) heavy cream
1 cup (225 ml) powdered sugar
Carmel Frosting:
Combine brown sugar, butter and cream, in a heavy sauce pan, cook until bubbles form around edges of the pan.
Remove from heat and add the powdered sugar, beating well.
Cool before spreading on the cake.
A simple and delicious one I got from here awhile back:
1 softened block of creamed cheese
1 jar of caramel ice cream topper
about 1c of powdered sugar
Mix together the creamed cheese and caramel topping until smooth. Then add in the powdered sugar and mix well. The first time I used almost the whole cup of sugar and found it to be too sweet. Since then, I use maybe 1/4c or none at all....depends on who it's for. I don't like things overly sweet, the caramel is sweet enough.
Everyone loves this.
That is so funny, because I am about to test some caramel recipes today. I think I am going to try a rum cake with the dulce de leche filling (boiled sweetened condensed milk) and then add some of the filling to the whimisical bakehouse BC to ice the outside of the cake. I will let you know how it turns out. Let me know if you test any good recipes!
fooby that is estrel's caramel cake...the chiffon cake is very light and the caramel frosting is very soft and it melts in your mouth..the caramel is also not sweet...it kind of like a custardy caramel frosting.
mbarbi, I never heard of this cake since I left the Philippines almost 3 years ago. Does the custard-like caramel frosting taste like leche flan? Mmmm I can taste it in my mouth now! 
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