Faults in cooking

Question 1

How to prevent lumps in a sauce

Answer 1

Stir all the time
Use moderate heat (not too hot)
For an all in one, make sure you dissolve flour in cold liquid (milk) before heating
For a roux sauce, add milk gradually not all at once

Question 2

How to prevent a cake from sinking

Answer 2

Do not open the oven door too early
Follow the method - whisk for long enough + cream for long enough
Use the correct flour (eg self raising not plain)
Do not add too much sugar
Do not add extra raising agent