Learn French: Mon assiette est vide, tu m'en sers encore ? - My plate is empty, are you serving me some more of it?

m'en combines me (to me) and en (some of it). When you have a double object pronoun with en, the indirect object pronoun (me, te, lui, nous, vous, leur) always comes first. Here, the e in me is dropped because en starts with a vowel.

Why is it mon assiette if the word assiette is feminine?

You're right that assiette is feminine, but it starts with a vowel sound. To make pronunciation flow smoothly and avoid the awkward pause in 'ma assiette', French uses the masculine possessive adjective mon before feminine nouns that begin with a vowel or silent H.

Doesn't encore usually mean 'again' or 'still'?

It does! However, when you are talking about quantities, portions of food, or drinks, encore is commonly used to mean 'more' or 'some more'.

Why is the present tense tu sers used to ask someone for something?

In conversational French, the present tense is frequently used to make immediate requests or ask for casual favors. It translates naturally here to 'are you serving me some more?' or 'will you serve me some more?' without needing to use the formal future tense.