1. Make cookies: Preheat oven to 350 degrees. Line baking sheets with Silpat nonstick baking mats or parchment paper; set aside. Sift flour, cocoa powder, malt powder, baking soda, and salt together into a medium bowl; set aside.

2. Put sugar and butter in the bowl of an electric mixer fitted with the paddle attachment; cream until pale and fluffy. Mix in egg and vanilla. Mix in creme fraiche. Mix in 3 tablespoons hot water. On low speed, mix in flour mixture.

3. Drop dough onto lined sheets with a 1/2-ounce-capacity ice-cream scoop, about 3 1/2 inches apart (or use a tablespoon; gently shape dough into balls). Bake until tops flatten and cookies are just firm, 10 to 12 minutes. Transfer to a wire rack; let cool completely.

4. Make filling: Melt chocolate and butter in a heatproof bowl set over a pan of simmering water, stirring occasionally until smooth. Let cool until just warm.

5. Put malt powder and cream cheese in a clean mixing bowl; return to mixer. Mix on medium until completely smooth. Gradually mix in half-and-half, then mix in melted chocolate and the vanilla. Refrigerate until thick, about 30 minutes.

6. Return bowl to mixer; mix on high speed until fluffy, about 3 minutes.

7. Assemble cookies: Spread a heaping tablespoon of filling on one cookie with an offset spatula. Press bottom of a second cookie onto filling. Repeat.