Learn Italian: Questa ricetta è molto facile.

In this sentence, molto is an adverb meaning "very," and it describes the adjective facile. Adverbs never change their endings. Molto only changes to molta, molti, or molte when it acts as an adjective describing a quantity of a noun, like in molta pasta (a lot of pasta).

Why does facile end in -e instead of -a if ricetta is feminine?

Adjectives like facile or intelligente belong to a group that always ends in -e in the singular. They use the exact same form for both masculine and feminine nouns. In the plural, the ending changes to -i, so "very easy recipes" would be ricette molto facili.

How would I change this to say "That recipe is very easy"?

You would replace Questa with Quella. While questa means "this" (close to the speaker), quella means "that" (further from the speaker). Both change their endings to match the feminine singular noun ricetta.