Line a 9-by-5-inch loaf pan with 2 sheets of plastic wrap, with long sides overhanging by about 3 inches. Arrange 3 wafers, flat side up, in a row in the bottom of the pan.
In a large bowl, beat mascarpone and sugar until light and fluffy. Stir in vanilla. In another bowl, beat cream until it holds soft peaks. In three additions, fold the whipped cream into the sweetened mascarpone with a rubber spatula.
In a bowl, mix 1 1/3 cups mascarpone mixture with toffee bits. In a separate bowl, mix another 1 1/3 cups mascarpone mixture with chocolate and cocoa powder. Dissolve the coffee in 1 teaspoon hot water; stir into the remaining mascarpone mixture.
Spread coffee mixture in prepared pan. Cover with 8 wafers, overlapping if necessary. Spoon chocolate mixture into pan; cover with 8 wafers. Spoon toffee mixture into pan.
Wrap pan with overhanging plastic; freeze at least 4 hours and up to 2 weeks. To serve, invert onto a serving platter. Remove plastic. Let terrine sit 5 minutes, then cut into slices.
Don't over mix the mascarpone - it will curdle. I used the paddle on my mixer rather than the whisk the second time I mixed it. It worked better that way for me.
This is a great summer recipe. It's decadent without having to heat up the oven. It makes a lot of dirty dishes, but it's not difficult to make. If you don't have chocolate wafer cookies on hand, I just scraped the cream filling out of some Oreos and they worked great. For my family the coffee flavor was too strong. Next time I may use some International House flavored coffee to make it milder. I will also experiment with other flavor options.
What a luxurious dessert!! I have made this a number of times. My family never tires of it. Takes a little time but so worth it.