Melt the butters by combining the butter and peanut butter in a microwave-safe bowl. Microwave for 30 seconds on high, then stir until smooth and fully melted. Let the mixture cool for about 5 minutes.

Incorporate eggs and vanilla by whisking in the eggs one at a time, ensuring each is blended before adding the next. Follow with vanilla extract until you have a smooth batter.

Combine dry ingredients by whisking together flour, sugar, baking powder, and salt in a separate bowl. Gradually fold this dry mixture into your wet ingredients until just combined.

Prepare the brownie base by pouring the brownie batter into a greased 9x13 inch pan, spreading it evenly. Bake at 350°F (175°C) for 20-25 minutes.

Make the crumb topping by mixing salted butter, flour, sugar, and cinnamon until crumbly. This mixture will provide a contrasting texture to the fudgy brownie base.

Bake the crumb mixture by spreading it across a second lined 9x13 inch pan and baking in the oven at 350°F (175°C) for about 15 minutes.

Add the chocolate layer by melting bittersweet or semisweet chocolate chips in the microwave for about 30 seconds, then pour it over the cooled brownie layer.

Layer the crumb cake by gently sprinkling the cooled crumb mixture over the chocolate layer and refrigerate for about 1 hour until set.

Slice and serve by removing the cake from the refrigerator and cutting it into bars. Sprinkle with powdered sugar for presentation.