Combine the finely ground chocolate graham crackers, melted butter, and sugar in a bowl. Press this mixture firmly into the bottom of your tart pan to create a sturdy crust.

Bloom the gelatin by sprinkling it over cold water in a small bowl. Allow it to sit for about 5 minutes until it swells and softens.

Melt the white chocolate chips with milk in a saucepan over low heat. Stir gently until the mixture is smooth and fully combined, taking care not to let it burn.

Dissolve the bloomed gelatin into the melted white chocolate mixture. Add in the powdered sugar, stirring until everything is silky and well-mixed.

Whip 1 cup of heavy whipping cream in a separate bowl until soft peaks form. Gently fold this whipped cream into the chocolate mixture along with the peppermint oil for a delightful burst of flavor.

Pour the luscious mousse filling into the prepared crust, spreading it evenly. Refrigerate for at least 2 hours or until set, letting all those flavors meld beautifully.

Prepare the ganache by heating chopped dark chocolate with light corn syrup and very warm water in a saucepan. Stir until smooth and shiny.

Cool the ganache slightly before pouring it over the set mousse tart, making sure every corner is covered to create a beautiful finish.

Chill the entire tart for another 30 minutes to allow the ganache to set before slicing and serving.