In a small bowl, combine brown sugar, nuts, cocoa powder, cinnamon, and coffee crystals; set aside.
In a mixer bowl, beat butter on medium speed of an electric mixer for 30 seconds. Add the sugar and vanilla; beat until fluffy. Add eggs, one at a time, beating well after each addition. Add Bisquick and yogurt alternately to beaten mixture, stirring just until combined.
Spoon about half of the batter into a greased 8-inch square baking pan. Sprinkle nut mixture on top. Spoon remaining batter over all. With a narrow spatula, swirl to marble. Bake in a 350°F oven for 35 to 40 minutes, or until done. Cool slightly on a wire rack. Dust lightly with powdered sugar.