Use a bittersweet chocolate in the 70% range.
Preheat the oven to 350F with a rack in the middle. Butter an 8x8-inch baking dish, or equivalent.
In a tiny cup combine the extract and ground cardamom. You should have about 1 teaspoon of freshly ground cardamom. Set aside.
Construct a double-boiler by arranging a stainless steel mixing bowl over a small pot of simmering water. Place the butter in the mixing bowl and allow to melt. Turn off the heat, and stir in the chocolate, mixing until fully smooth and melted. Water is the enemy of melted chocolate so, avoid getting water or a steam in your chocolate bowl. Set aside.
Pour the batter into the prepared baking dish and bake until the edges look dark and done, and the top looks glossy with some cracking, about 25 minutes. The center should offer some structured resistance, no jiggling. Cool completely on a wire rack, cover with plastic wrap, and refrigerate overnight. These are good straight out of the oven, cooled a bit, but transcendent if you can hold off until the next day.
Makes 20 deep-dish brownies