The most common and most likely answer to this crossword clue is the 7 plus 7 letter word PANCAKE MAKE-UP
P
A
N
C
A
K
E
M
A
K
E
-
U
P
Buddy explains!
The straight part
We know that "foundation" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case foundation = pancake make-up.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.