1/3 cup Dutch-processed cocoa
1 1/2 teaspoons instant espresso (optional)
1/2 cup plus 2 tablespoons boiling water
2 ounces unsweetened chocolate, finely chopped
4 tablespoons (1/2 stick) unsalted butter, melted
1/2 cup plus 2 tablespoons vegetable oil
3 large eggs
2 teaspoons vanilla extract
2 1/2 cups sugar
1 3/4 cups unbleached all-purpose flour
3/4 teaspoon table salt
12-16 empty egg shells, reserve yolks/whites for another recipe (include the 3 eggs in the recipe)
Prepare egg shells by carefully poking a small hole in bottom of each egg using a corkscrew, nail or large needle. Open the hole up so the tip of a piping bag can be inserted. Insert a wooden skewer to break up the yolk, then shake out the contents into a bowl (collect 3 separately to use in the recipe).
When egg shells are all emptied, rinse them well and place them in a large container of salt water (hold them under to fill them with water so they sink). Soak about 30 minutes, then rinse and turn upside down on paper toweling to drain.
Using a funnel, put about 1 teaspoon of vegetable oil in each shell. Gently shake to distribute and turn upside down to drain any excess. Set aside to make batter.
Preheat oven to 350F.
Whisk cocoa, espresso powder (if using), and boiling water together in large bowl until smooth. Add unsweetened chocolate and whisk until chocolate is melted. Whisk in melted butter and oil. Add eggs, yolks, and vanilla and continue to whisk until smooth and homogeneous. Whisk in sugar until fully incorporated. Add flour and salt and mix with rubber spatula until combined.
Place eggs, hole side up, in mini muffin tin, using aluminum foil nests to keep upright. Put batter into a piping bag fit with a round tip. Fill the eggs about 2/3 full with batter. Gently clean any batter off of shells with a damp cloth. Bake about 35-38 minutes. Remove any overflow when brownies are still warm and wipe with damp cloth.
Cool, remove top of shell or all of shell to serve. Decorate, if you are playing Easter Bunny with them.