Are you meant to drizzle the finished dish with the morel herb butter? Or is it added at an earlier stage?

The recipe author states in the headnotes, "However, one night I slid a pat of frozen Morel Herb Butter under the chicken skin and discovered a date night version." So I would make the butter and freeze, then make the recipe as written. So you're basically making a compound butter to slip under the skin while it cooks.