Learn Swedish: Ett intensivt fräsande började när fettet blev varmt. - An intense sizzling started when the grease became hot.

Fräsande is the present participle of the verb fräsa (to sizzle/hiss). By placing ett before it, we turn it into a neuter noun. This nominalization emphasizes the continuous, ongoing nature of the action, much like the English gerund 'sizzling'.

Why does the adjective intensivt end in an -t?

Because it modifies the nominalized participle fräsande. When you turn a present participle into a noun to express a continuous action, it always becomes a neuter noun (an ett word). Adjectives describing it must take the neuter -t ending.

Why is varmt in the neuter form even though it is separated from its noun?

Adjectives must agree with the noun they describe, regardless of their position in the sentence. Because fettet (the fat/grease) is a neuter noun, the predicative adjective following the verb blev (became) must take the neuter -t ending to become varmt.

In what other contexts would I see or hear the word fräsa?

While it perfectly describes fat sizzling in a pan, fräsa is also the verb used for a cat hissing. You can also use it metaphorically for a person who snaps or speaks very angrily to someone else.