Position a rack in the upper third of the oven and preheat to 350 degrees Fahrenheit. Line the baking pan across the bottom and up all four sides with foil.

For the chocolate layer, place the butter and chocolate in a medium stainless steel bowl set directly in a wide skillet of barely simmering water. Stir frequently until chocolate is completely melted and the mixture is smooth and quite hot. Stir in the sugar and remove from the heat.

In a separate bowl, use a large spoon or spatula to mix all of the ingredients for the peanut crunch layer until completely blended. Press the mixture evenly in the bottom of the prepared pan. Bake for eight to 10 minutes, until it is slightly darker at the edges.

Remove the pan from the oven and spoon dollops of chocolate batter all over the hot crust. Spread gently to make an even layer.

Use a large spoon to beat in the eggs, vanilla, and salt. The mixture should be very smooth; if it is not, place the bowl back in the water bath over very low heat for 30 seconds, stirring constantly.

Add the flour and beat with a spoon until the batter comes away from the sides of the bowl, about one minute. Set aside.

Return the pan to the oven and bake for 20 to 22 minutes, until the surface is dry and pulls away slightly from the sides of the pan. Cool completely in the pan on a rack. Lifting the edges of the foil, transfer the brownies to a cutting board. Cut into 25 squares.