Answer:
Because my porridge had gone cold.
Step-by-step explanation:
The dependent clause in this sentence is 'Because my porridge had gone cold'.
Dependent clause -
A group of words that don't make sense unless it's combined with the independent clause.
Most of the time dependent clauses don't give sense because of the conjunctions attached to them.
Independent clause -
A group of words that makes sense in its own.
I heated the microwave.
The above sentence makes sense.
Because my porridge had gone cold.
It doesn't make any sense.