Preheat oven to 325 degrees and grease and flour a 8X8-inch baking pan.
In a medium saucepan, melt the butter and chocolates over low heat, stirring frequently. Once smooth, remove from heat and allow to cool for 5 minutes.
Place the eggs and sugar in a large bowl and whisk until light and creamy, about 2 minutes.
Whisk in vanilla extract.
Gradually (so that eggs do not curdle) whisk in chocolate mixture.
Switch to a wooden spoon or rubber spatula and mix flour and salt into the chocolate mixture.
Stir in half of the pecans and half of the butterscotch chips.
Pour batter into prepared pan and bake for 20 minutes.
Remove from oven and sprinkle remaining pecans and butterscotch chips on top.
Return pan to oven for 15-20 more minutes. Cool to room temperature before cutting.
Notes
To toast pecans, place on a baking sheet in a 350 degree oven for about 10 minutes. They should be lightly browned and fragrant.