By “sharp,” I assume you mean “good-looking.” First of all, remember that current ideas about “thank-you notes” are skewed. “Notes” are not appropriate for conveying gratitude, particularly when written on notepaper pre-printed with the words “Thank You.” If you must use notepaper because you do not have access to letter-sized stationery, then use a notecard that has an attractive design on the front, a blank inside for your handwritten letter, and does not have any pre-printed wording. Although not easy to find these days (since stationery suppliers often assume “Thank You” cards are appropriate), you can usually find nice blank notecards displayed nearby wherever “Thank You” cards are sold. That said, stationery is more appropriate.
As for writing the thank you for a bishop, all you do is adapt how you would ordinarily write a thank you. Address him as “Your Excellency”; do not open with the words, “Thank you for…” (because it sounds as if you’re issuing a receipt); and tell him what an honor it was for your parish to have him visit on its anniversary. Close with “Very truly yours” (because this is business correspondence) and add “… in Christ” if you like.
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