The Invariable Participle with "en"
When a direct object comes before a verb in a compound tense, the past participle usually agrees with it. However, if that preceding direct object is the pronoun en (meaning "some" or "of it/them"), the past participle is invariable. It stays in its base masculine singular form, no matter what noun en is replacing.
| Walnuts? I chopped some for the cake. | Des noix ? J'en ai haché pour le gâteau. |
| Spices? I added some in the frying pan. | Des épices ? J'en ai ajouté dans la poêle. |
Even though noix and épices are feminine plural, haché and ajouté do not take an -es because the direct object is en.
Specific Quantities and Portions
When cooking, you often pair en with specific numbers or measurements at the end of the sentence to say exactly how much of an ingredient you used.
Even when en is accompanied by a quantity (like trois or beaucoup), or a feminine noun of measurement (like une douzaine or une pincée), the rule does not change: the past participle remains invariable.
| Leeks? I peeled three of them. | Des poireaux ? J'en ai épluché trois. |
| Olives, I chopped a dozen of them. | Des olives, j'en ai haché une douzaine. |
| Salt? I added a pinch of it. | Du sel ? J'en ai ajouté une pincée. |
| I added two spoonfuls of it and I stirred. | J'en ai ajouté deux cuillerées et j'ai remué. |