Step 1
Preheat oven to 325 degrees F (165 degrees C).
Step 2
Grease an 8-inch baking pan with 1 teaspoon butter. Add cocoa powder; move pan around to spread evenly. Turn pan upside down over the sink; tap gently to remove excess cocoa. Place baking pan inside a larger baking pan.
Step 3
Place chocolate 1/4 cup butter and coconut oil in top of a double boiler over simmering water. Stir frequently scraping down the sides with a rubber spatula to avoid scorching until chocolate is almost completely melted 4 to 5 minutes. Remove from heat.
Step 4
Bring 4 cups water to a simmer in the same saucepan from the double boiler.
Step 5
Whisk eggs and sugar together in a large bowl. Mix vanilla extract and espresso together in a separate bowl until espresso is dissolved. Pour vanilla extract mixture into egg mixture. Add salt. Stir in cooled chocolate mixture.
Step 6
Pour chocolate batter into the prepared 8-inch pan. Pour simmering water into the larger baking pan to create a hot water bath.
Step 7
Bake brownies in the water bath in the preheated oven until a toothpick inserted into the center comes out mostly clean with a few crumbs attached 52 to 55 minutes.
Step 8
Remove 8-inch pan carefully from the hot water bath. Invert onto a wire rack lined with parchment paper. Cool for 30 minutes. Refrigerate until firm about 3 hours. Cut into squares and sprinkle with confectioners' sugar.