Headers for my static library not found

I have a static library iOS project ProjectCore, that I want to include in the project MyProject.

In the library project I set:

PUBLIC_HEADERS_FOLDER_PATH = $(TARGET_NAME)

So I end up with the following structure

libProjectCore.a
ProjectCore (Folder)
+- ProjectCore.h
+- ProjectCoreUtil.h

In the directory /.../DerivedData/MyProject-xyzabcd/Products/Release-iphoneos/

Now I setup MyProject

• Add ProjectCore as a git submodule next to MyProject.xcodeproj
• Drag the ProjectCore.xcodeproj to Xcode
• Add the project as a dependency
• Link against libProjectCore.a
• I set it's "Header Search Path" to $(BUILT_PRODUCTS_DIR) which should point to the folder above.

Curiously neither of the approaches work:

#import "ProjectCore.h" // With the (Recursive Flag set for the Headers)
#import <ProjectCore/ProjectCore.h> // The way RestKit does it