In a saucepan combine 1 1/2 cups of the cream and the mint and bring to a boil. Remove from the heat and let cream infuse for at least 1 hour and up to 2 hours. Place white chocolate chips in a large bowl and return mint-infused cream to a boil. Strain hot cream through a fine sieve into the bowl containing the white chocolate. Let sit for 1 minute, then whisk until smooth. Transfer to the refrigerator to cool, stirring occasionally. Place semisweet chocolate chips in another bowl and heat remaining cream in a saucepan to a boil. Pour over semisweet chocolate and let sit for one minute, then whisk or stir until smooth and thick. Transfer to the refrigerator and stir occasionally until thoroughly chilled. When both mixtures are cold and thickened, beat with an electric mixer to soft peaks, then beat the last few strokes by hand with a whisk until thick and firm. (Be careful not to overwhisk, or mixture will become grainy.)

Line an 8- by 4-inch bread pan or terrine mold with aluminum foil, smoothing to remove as many wrinkles as possible. Using a spatula, place an even layer of the dark chocolate ganache on the bottom of the prepared terrine mold, using about one quarter of the entire volume. Place the terrine in the freezer for 5 to 10 minutes, until the layer of ganache is firm. Top the first layer with a layer of the white chocolate ganache, using about one third of the entire volume. Chill until firm, then repeat with remaining white and dark chocolate ganaches, alternating layers of each mixture. When terrine is completely assembled, cover and refrigerate at least 3 hours or overnight before unmolding. Remove terrine by pulling overhanging aluminum foil out of the mold. Carefully “peel” aluminum foil off of terrine, then slice using a warm, damp knife. Serve with Chocolate Fudge Sauce.

CHOCOLATE FUDGE SAUCE: In the top of a double boiler, melt chocolate chips over simmering water. When chocolate begins to melt, whisk in heavy cream and water. Remove from heat when smooth, and stir in the Grand Marnier. Serve sauce either warm or at room temperature.

Yield: 1 generous cup of sauce, serving 8 to 10.