Generously grease two 8-inch round cake tins. Cut circles of parchment paper to fit the bottoms of the tins. Grease tops of paper.
Melt 1 1/2 cups brown sugar, 1/2 cup milk, and chocolate in a pan over low heat, stirring constantly, until smooth. Take pan off heat and set aside to cool.
In a large bowl, cream the butter and remaining one cup of brown sugar until light and fluffy. Add remaining 1/2 cup of milk and the vanilla, whisking until batter is smooth.
In a smaller bowl, sift together the flour and baking soda.
Gradually add the dry ingredients to the butter mixture, stirring until fully incorporated.
Add the cooled chocolate mixture to the batter and stir. The batter will be fairly stiff.
Divide the batter evenly between the two prepared cake tins, using a spatula to smooth down the surface of the batter as well as you can.
Bake for about 30 minutes, or until a toothpick inserted into the center of one of the brownies comes out clean.
Cool in tins on wire racks until pans are cool to the touch. Turn the brownies out into your hand, one at a time, placing each bottom-side down on the wire rack to cool completely.
Frosting Instructions
Whisk the confectioner’s sugar into the cream a little at a time. Chill for about 10 minutes.
When brownies are completely cool, spread frosting evenly across the top of one. Place the second brownie on top of the icing. Serve in slices.
Notes
This recipe was written by Marie Kelly in 1899. It's been reworded for the modern audience.