Pastry (Steps 1 through 4) can be prepared, frozen, removed to a freezer bag and frozen up to 2 months. To bake, don’t defrost; add about 10 minutes to baking time. The assembled and glazed ring can be refrigerated up to 8 hours.
Heat oven to 425°F Line a baking sheet with parchment paper and have ready 1 gallon-size ziptop bag and a pastry bag fitted with a large star piping tip. Draw an 8-in. circle on the parchment paper; turn paper over.
Bring milk, water, butter, sugar and salt to boil in a medium saucepan over medium-high heat. Add flour all at once; stir energetically with a wooden spoon until dough comes together in a shiny mass (bottom of pan will be covered with a thin film of flour). Cook, stirring constantly, 1 to 2 minutes. Transfer hot dough to a large bowl.
Using a sturdy mixer, beat in eggs, 1 at a time, until each is blended (dough will be thick and shiny). Spoon warm dough into a ziptop bag; cut 3/4 inches off 1 corner.
Pipe a ring about 1 inches thick on circle on parchment paper. Pipe a second ring inside first, just touching first ring. Pipe a third ring on top where rings meet. (If there’s extra dough, pipe mounds for cream puffs or strips for eclairs.)
Bake 20 minutes, reduce oven temperature to 375°F and bake 20 to 25 minutes more until puffed, brown and firm. Transfer sheet to a wire rack; let ring cool completely. (Ring will sink; that’s OK.).
Strain cream into a measuring cup, adding more chilled heavy cream if needed to make 1 1/3 cups. Pour into a large bowl, add 1/4 cup sugar and beat with mixer on medium speed until stiff peaks form when beaters are lifted. Stir remaining 2 Tbsp sugar into crème fraîche; gently fold into whipped cream.
Using a serrated knife and gentle sawing motion, slice top off pastry ring. Pull out and discard soft dough inside base. Carefully transfer base to a serving platter.
Spoon cream filling into prepared pastry bag. Pipe large rosettes close together into base. Pipe another row of rosettes on first row, piping top rosettes between bottom rosettes. Add pastry top. Refrigerate while making Glaze.
Microwave chocolate, cream and corn syrup in small bowl on high, stirring every 10 seconds until chocolate melts and glaze is smooth. Spread on top of pastry ring; sprinkle with almonds. Refrigerate at least 1 hour or up to 8 hours before serving.