In a large bowl, with a mixer on medium speed, beat butter and sugar until smooth. Add egg yolk and beat until well blended.
In a medium bowl, mix flour, ground coffee, baking powder, and salt. Stir into butter mixture, then beat until well blended. Press dough level in bottom of a 9- by 13-inch baking pan.
Bake crust in a 325° regular or convection oven until lightly browned, 15 to 18 minutes. Spread the warm crust with marmalade, then let cool completely.
Meanwhile, in a heatproof bowl set over (but not touching) barely simmering water in a pan, stir chocolate and cream often until chocolate is melted and mixture is smooth. Spread evenly over marmalade and chill until chocolate mixture is firm to touch, about 30 minutes. Cut into 24 bars.
Nutritional analysis per bar.