for the brownies: Preheat oven to 325° F. Fold a long piece of heavy foil into a 13" wide strip and fit it inside a 9" x 13" metal baking pan, leaving foil overhang on the 2 long sides. Spray the foil lightly with nonstick spray. Set pan aside.

In a large heavy saucepan over very low heat, stir butter and chocolate until everything is melted. Remove from heat and whisk in the sugar, and then the eggs, one at a time. Whisk in espresso powder, vanilla, and salt. Then sift the flour over the chocolate mixture and stir to blend well. Transfer batter to prepared pan.

Bake brownies until slightly puffed and dry-looking and tester inserted into center comes out with some moist batter attached, about 20 minutes. Let cool completely in pan on rack.

for the fresh raspberry buttercream: In a medium saucepan over medium heat, cook the raspberries, stirring frequently, until the raspberries are broken down into a very loose sauce. Line a fine mesh strainer with a double layer of cheesecloth, and then pour the raspberry sauce through to remove the seeds. To get all the raspberry juice possible, twist up the ends of the cheesecloth very tightly and press on the raspberry sauce with the back side of a large wooden spoon to extract the juice. Then pour the raspberry juice back in the pot. Simmer until the juice reduces to 1/4 cup. The juice will be very concentrated, deep red in color. Set aside to cool.

to create the brownie hearts: Run a knife around the inside edge of the brownie pan. Use the overhanging foil as an aid and gently lift the brownies from the pan. The brownies should be about 1/2" thick, so ensure that your cookie cutter is taller than 1/2". Press heart-shaped cookie cutters (the cookie cutters used in my photos measure 3" wide and 1-1/2" wide) firmly into the cooled brownie. Use a thin metal spatula to lift the cookie cutter filled with brownie from the foil. Gently press the brownie out of the cookie cutter. Repeat the cutting process until your brownie looks like a big piece of Swiss cheese. (Don't throw away the scraps, they're awesome little nibbles!)

With the pastry bag filled with fresh raspberry buttercream, pipe a line of frosting around the inside edge of one of the brownie hearts. Then fill in the inside of the line with frosting, too. Top with another brownie heart, gently pressing down to make a sandwich. Repeat until all your brownie hearts are completed.

With the heart-shaped cookie cutters I use, I can make six large brownie heart sandwiches, plus several smaller ones. Or I can make about 20 of the smaller brownie heart sandwiches.