Learn Danish: Manden købte et håndbygget mekanisk ur. - The man bought a hand-built mechanical watch.

In Danish, adjectives ending in -isk are a notable exception to the usual rules. They never add a -t in the neuter singular indefinite form. Therefore, it remains et mekanisk ur.

How does the word håndbygget get its ending here?

It is a compound of hånd (hand) and the past participle of at bygge (to build). Because it ends in -et, this participle uses the exact same form for both neuter and common gender indefinite nouns. It only changes to håndbyggede if the noun becomes definite or plural.

How would I apply this lesson's target grammar to say 'the ever so hand-built mechanical watch'?

You would change the object to det nok så håndbyggede mekaniske ur. Notice that when you use the definite article det alongside nok så, both adjectives must take their definite -e endings.

Why use et ur instead of en klokke?

Et ur refers specifically to a timepiece, such as a wristwatch or a wall clock. En klokke refers to a bell. While you hear the word in the phrase hvad er klokken? (what time is it?), the physical object you wear or look at is always et ur.