01 -
Preheat oven to 350°F (175°C). Line two baking sheets with parchment paper.
02 -
In a stand mixer with paddle attachment, beat unsalted butter and granulated sugar on medium-high until light and fluffy, about 2 to 3 minutes, scraping down the sides as needed.
03 -
Add egg, light corn syrup, and vanilla extract to the butter mixture. Beat until well combined. Scrape down the bowl.
04 -
In a separate bowl, whisk together all-purpose flour, unsweetened cocoa powder, cornstarch, baking soda, and fine salt.
05 -
On low speed, gradually add the dry ingredients to the wet mixture. Mix just until combined; dough should be soft and slightly sticky.
06 -
Using a 1 1/2-tablespoon cookie scoop, portion dough onto prepared baking sheets. Bake for 8 to 9 minutes until just puffed and edges are set. Cool slightly, then transfer cookies to racks to cool completely. Cookies will flatten as they cool.
07 -
Place milk chocolate chips and vegetable oil in a microwave-safe bowl. Microwave in 15-second intervals, stirring between each, until melted and smooth.
08 -
Drizzle or pipe melted chocolate over each cooled cookie. Refrigerate for at least 30 minutes until chocolate is fully set.
09 -
In a stand mixer, beat unsalted butter on medium speed until smooth. Add sifted cocoa powder and powdered sugar; beat until light and fluffy, about 3 minutes, scraping sides as needed. Add warm water and vanilla, beating on medium-high until filling is smooth and airy, about 2 minutes.
10 -
Pipe or spread filling onto the flat side of half the cookies. Gently press a second cookie on top to form sandwiches.
11 -
Store assembled fudge rounds in an airtight container: up to 1 day at room temperature, up to 5 days refrigerated, or freeze for up to 1 month. Serve cold for enhanced fudgy texture.