Combine butter and chocolate pieces in a microwave safe container (I use a Pyrex measuring cup).
Microwave on high for 45 seconds to one minute, depending on how powerful your microwave is.
Microwave again for 30 seconds.
Repeat process as needed until chocolate is thoroughly melted and combined with butter. If you stir thoroughly each time, the chocolate will continue to melt. Total micro time shouldn't be more than a few minutes, you don't want to overcook the chocolate.
Cool to room temperature.
Beat eggs and sugar with an electric mixer until thickened and pale.
Beat in chocolate mixture and Sambuca.
Combine dry ingredients except for pine nuts in a small bowl.
Add to batter and beat until just blended.
Spread batter in prepared pan.
Sprinkle evenly with the pine nuts.
Bake for 30-35 minutes, or until a cake tester comes out with crumbs just barely sticking to it.