Lightly grease a 9-inch square pan. Line the pan with waxed paper, smoothing out any wrinkles.

Combine semisweet chocolate and 1 teaspoon canola oil in the top of a double boiler over just barely simmering water. Stir frequently, scraping down the sides with a rubber spatula to avoid scorching, until chocolate is melted. Remove from the heat and stir in 1/4 teaspoon peppermint extract.

Pour melted chocolate into the prepared pan, and spread evenly to cover the bottom. Sprinkle 1/2 of the crushed candy over the chocolate and refrigerate until completely hardened, about 1 hour.

Combine white chocolate and remaining 1 teaspoon canola oil in the top of a double boiler over just barely simmering water. Stir frequently, scraping down the sides with a rubber spatula to avoid scorching, until white chocolate is melted. Remove from the heat and stir in remaining 1/4 teaspoon peppermint extract.

Pour melted white chocolate into the pan, directly over the hardened chocolate layer; spread evenly. Sprinkle the remaining crushed candy over top and gently press in. Refrigerate until completely hardened, about 1 hour.

Remove from the pan and break into small pieces to serve.