Preheat your oven to 350°F. Grease a 9-inch pie dish lightly with butter or spray. This helps the brownie pie release easily after baking and keeps the edges from sticking.

In a large bowl, add melted butter, granulated sugar and brown sugar. Whisk well until smooth. The mixture should look glossy and slightly thick after mixing.

Crack the eggs into the bowl. Add vanilla extract. Whisk again until fully combined. The batter should look creamy and slightly fluffy after mixing for one minute.

In another bowl, mix flour, cocoa powder, salt and baking powder. Stir gently to remove lumps. This helps the dry ingredients blend evenly in the batter.

Slowly add the dry ingredients into the wet mixture. Stir with a spatula until smooth. Do not overmix. The batter should be thick and rich.

Fold in the chocolate chips and chopped walnuts. These add texture and extra flavor. Mix gently so the chips spread evenly through the brownie batter.

Pour the batter into the prepared pie dish. Spread it evenly with a spatula. The batter will be thick, so smooth the top carefully.

Place the pie dish in the oven. Bake for about 35 minutes. The top should look shiny and slightly cracked. The center should stay soft and fudgy.

Remove the pie from the oven. Let it cool for at least 20 minutes. This helps the brownie pie set properly before slicing.

Dust the top lightly with powdered sugar if desired. Cut into slices and serve warm. You can also add ice cream for a special dessert.