Make dough: Whisk together flour, cocoa powder, baking powder, and salt.
Beat butter and sugar with an electric mixer until pale and fluffy, then beat in yolk and vanilla. At low speed, mix in flour mixture in 3 batches just until a dough forms. Divide dough in half and form each piece into a 6-inch square, then chill, wrapped in plastic wrap, until firm, 2 to 3 hours.
Make ganache while dough chills: Bring cream and corn syrup just to a simmer in a small heavy saucepan, then stir into melted chocolate. Stir in butter and vanilla until smooth. Cover surface with parchment paper and chill, stirring occasionally, until very thick, about 30 minutes.
Cut and bake cookies: Preheat oven to 350°F with rack in middle. Butter 2 large baking sheets.
Roll out 1 piece of dough between sheets of parchment paper into a 14- by 10-inch rectangle (1/8 inch thick). Slide dough in parchment onto a tray and freeze until dough is firm, about 10 minutes. Repeat with remaining dough.
Cut out as many rounds as possible from first chilled square with cutter, reserving and chilling scraps, then quickly transfer cookies to a buttered baking sheet, arranging them 1/2 inch apart. (If dough becomes too soft, return to freezer until firm.)
Sprinkle half of cookies with decorative sugar (if using), then bake cookies until baked through and slightly puffed, 10 to 12 minutes. Cool on sheet on rack 5 minutes, then transfer to rack to cool completely (cookies will crisp as they cool).
Make more cookies with remaining dough and scraps (reroll only once).
Assemble sandwich cookies: Beat ganache with an electric mixer at high speed just until light and fluffy. Transfer to a sealable plastic bag (snip off 1/8 to 1/4 inch from 1 corner with scissors). Pipe ganache onto flat sides of plain cookies, then top with sugared cookies to make sandwiches. Chill, layered between sheets of parchment, in an airtight container until filling is set, at least 1 hour.
Cook's notes: · Dough can be chilled up to 2 days. · Ganache can be made 1 day ahead and chilled, its surface covered with parchment. Bring to room temperature, then beat with mixer before using. · Sandwiched cookies keep, chilled, 4 days.

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Nutrition Facts

Per Serving Per 100 g

Amount Per 1 Serving
Calories	3425.16 Kcal (14340 kJ)
Calories from fat	2705.41 Kcal
		% Daily Value*
Total Fat	300.6g	462%
Cholesterol	783.58mg	261%
Sodium	567.74mg	24%
Potassium	970.83mg	21%
Total Carbs	178.36g	59%
Sugars	105.25g	421%
Dietary Fiber	6.82g	27%
Protein	23.4g	47%
Vitamin C	1.3mg	2%
Vitamin A	3.1mg	104%
Iron	3.5mg	20%
Calcium	389.3mg	39%

Amount Per 100 g
Calories	564.02 Kcal (2361 kJ)
Calories from fat	445.5 Kcal
		% Daily Value*
Total Fat	49.5g	462%
Cholesterol	129.03mg	261%
Sodium	93.49mg	24%
Potassium	159.87mg	21%
Total Carbs	29.37g	59%
Sugars	17.33g	421%
Dietary Fiber	1.12g	27%
Protein	3.85g	47%
Vitamin C	0.2mg	2%
Vitamin A	0.5mg	104%
Iron	0.6mg	20%
Calcium	64.1mg	39%

* Percent Daily Values are based on a 2000 calorie diet. Your daily values may be higher or lower depending on your calorie needs.
Find out how many calories should you eat.

Tastes

salty
savory
bitter
sweet

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