In a large pan, begin melting butter, stirring constantly. Keep stirring over medium-low heat until butter begins to smell nutty and has started to turn a golden brown color, about five minutes. Remove from heat, add in the ice cube and set aside.
In a large mixing bowl, beat together the eggs, vanilla and sugar until thick and a pale yellow color. Sift in the cocoa powder, espresso powder and salt and mix until well blended. Add in the browned butter and hen the melted chocolate, mixing well after each addition. Sift in the flour and mix well.
In a bowl, combine the 3.5 ounces chopped milk chocolate, 3.5 ounces chopped 75% cacao chocolate and 6 ounces semi-sweet chocolate chips. Fold HALF of the chocolate into the brownie batter, reserving the remaining chocolate.
Line an 8x11 pyrex pan (can also use a 9x13 pan, adjusting the bake time to 30 minutes) with parchment paper. Spread the batter into the prepared pan. it will be VERY thick. Scatter remaining chocolate over the top of the batter and cover tightly with plastic wrap. Set in fridge for three days.
On the third day, preheat oven to 350 degrees. Remove pan from fridge and remove plastic wrap. Bake at 350 for 35 minutes (30 if using 9x13 pan).
After baking, remove pan from the oven and immediately top with aluminum foil. Place pan in the freezer for 30 minutes.
After 30 minutes, transfer pan to fridge for 24 hours.
When ready to serve, remove pan from fridge, remove brownies from pan and slice into 12 portions. To eat, warm each slice in the microwave for about 20 seconds or warm in a 350 oven for a couple of minutes. Eat, blissfully, with a large, cold glass of milk!
