If you're short on time, you can also fill these pies with whipped cream or traditional marshmallow fluff. The discs can be large or small.
3 ounces (90 grams) bittersweet chocolate, finely chopped
2/3 cup cocoa powder
1 3/4 cups boiling water
2 3/4 cups unbleached all-purpose flour
1 1/4 teaspoon baking soda
1/4 teaspoon baking powder
1 cup white sugar
1 cup packed brown sugar
1 1/3 cup full-fat mayonnaise
2 large eggs
1 teaspoon vanilla extract
3/4 cup unsalted butter, softened
4 cups icing sugar, sifted
1/4 cup salted caramel (recipe below)
Fleur de sel for sprinkling
Combine chocolate and cocoa powder in a medium heatproof bowl. Add boiling water and mix until smooth. Set aside.
Sift together flour, baking soda and baking powder in a medium bowl. Set aside.
Combine white sugar, brown sugar and mayonnaise in a stand mixer and blend until smooth (about 2 to 3 minutes). Add eggs one at a time, beating well after each addition and scraping sides as needed. Beat in vanilla. Add a quarter of flour mixture, blend in and add a third of chocolate mixture. Continue alternating, blending well after each addition. Chill for 1 hour or until mixture has firmed up slightly.
Preheat oven to 350 F.
Scoop tablespoon-sized mounds of batter onto a parchment-lined (or greased and floured) baking pan about 2 inches apart. Bake for 10 minutes or until a tester comes out clean. Cool. Repeat until you have used up all the batter.
Combine butter and icing sugar in a stand mixer fitted with the paddle attachment and blend until smooth. Slowly add salted caramel and mix until well blended. Chill until ready to use. If it hardens too much to spread, let it warm up slowly at room temperature.
Spread one chocolate disc with caramel filling and a sprinkle of fleur de sel. Top with another chocolate disc to make a sandwich. Repeat with remaining chocolate discs and filling. Chill for 30 minutes to set. Makes about 30.