To make the crust: Stir together the oats, flour, brown sugar and baking soda. Work in the butter or margarine until the mixture is crumbly. Reserve 3/4 cup of the oat mixture and press the remaining mixture in the bottom of a greased 9-by-13-inch baking pan. Bake in a 350 F oven for 15 minutes. (The crust still will be a little soft in the center.) Cool slightly on a rack.

To make the brownies: Beat together the butter and sugar until fluffy. Add the eggs and vanilla, mixing well.

Combine the flour and cocoa. Add to the butter mixture, beating until smooth.

Spread over the cooled crust and dot the top with the reserved crust mixture. Bake at 350 F for 30 to 35 minutes. (The brownies still will be a little soft in the center. If you like your brownies more cakelike, continue baking an additional 5 to 10 minutes.)

Cool the brownies on a rack and cut when completely cooled.