Learn Finnish: Äidin leipoma piirakka on todella maukas. - The pie baked by mother is really tasty.

In Finnish, when you use the agent participle (like leipoma), the person doing the action (the "agent") must be in the genitive case. Instead of saying "baked by mother", Finnish literally says "mother's baked".

How is the word leipoma formed from the verb leipoa?

Leipoma is the agent participle form of leipoa (to bake). You form it by taking the strong verb stem (leipo-) and adding the suffix -ma or -mä. This turns the verb into a descriptive word that acts like an adjective.

Why do äidin and leipoma come before the word piirakka?

Because participles behave just like regular adjectives in Finnish. Just as you would put the adjective before the noun in hyvä piirakka (good pie), you must put the whole participle phrase before the noun: äidin leipoma piirakka (the mother-baked pie).

Could I say this using a relative clause with joka (which/that) instead?

Yes! You could say Piirakka, jonka äiti leipoi, on todella maukas. (The pie, which mother baked, is really tasty). The agent participle is just a more compact, native-sounding way to express the exact same idea without needing a comma or a comma.