Any food combination which contains a main ingredient (ikkar) and a secondary ingredient (toffel), say the beracha on the ikkar and exempt the toffel. (ShA1)
Three criteria can be used to determine which is the ikkar:
Any of the 5 grains used for taste is always ikkar.
The main ingredient is ikkar if the others are there only to enhance it.
If the above two do not factor, go after the majority. (MB1)
A mixture is an example of a food combination. Say a beracha only on the ikkar even if the toffel food is clearly identifiable. (MB1)
But a food combination can also be two foods eaten one after the other. Example: You drink whiskey and then eat a piece of bread afterwards only to cut the sharp taste. If you had bread in mind when you blessed on the whiskey, the bread doesn’t need a beracha – it is toffel. Also, if you didn’t specifically have the bread in mind but you regularly eat something to cut the sharp taste of the whiskey, whatever you eat for that purpose will be toffel. (ShA1 – MB5)
In the above case, you will have to bless on the bread separately if your intention is to eat both the whiskey and bread for their own sake. This is the case when a sizeable amount of bread is eaten. Though, it could be the same with a bit of bread. (MB5 – ShaH19)
In cases that it is difficult to ascertain the purpose of bread (being toffel or ikkar) it’s best not to eat it. (MB5)
Sometimes you eat two delicious foods together but one is clearly only a secondary accompaniment (e.g. crackers with cheese or fish). The accompaniment is toffel. What’s more is that you will not say a separate beracha achrona on the accompaniment either. (MB6 – ShaH20)
Pas haboh b’kisnin is the ikkar when eaten with other foods. (MB6)
Sometimes you wish to eat the toffel food first before the ikkar – never do this as you will be entering into a major disagreement among the poskim regarding the beracha on the toffel. (MB10)