Share 'Making Semisweet chocolate from unsweetened chocolate'

I need a semisweet chocolate with very little sugar (somwhat bitter) for certain items (such as the bottoms of my coconut macaroons). This semisweet chocolate must be tempered. I usually use unsweetened chocolate, sugar, vanilla, cocoa butter, and regular butter. What should the ratio of butter to cocoa butter be to have enough cocoa butter crystals to temper the chocolate? Or should the amount o…