Pre-heat oven to 180°C. Pulse all ingredients in a food processor until the oats are coarsely grounded and the mixture resembles "wet sand".
Firmly press mixture onto the bottom and up the sides of the tart pan. Bake until the crust is golden brown. Transfer to a wire rack and allow it to cool.
Dissolve the espresso powder in 125 ml of hot water, add cocoa powder and set aside for 5 minutes. Add the California Raisin Paste, melted chocolate, vanilla extract, vegetable oil and salt to a food processor. Process for approximately 30 seconds or until the mixture is very smooth and thick.
Transfer filling into the cooled tart shell and smoothen the top. Tap tart lightly to remove any air bubbles.
Cook oats in 30 g of vegetable oil over low heat, stirring constantly, until the oats are toasted (approximately 3 minutes). Gradually add half of the demerara sugar. Stir until the sugar is melted, remove from heat and add the remaining demerara sugar and California Raisins. Set aside to cool.
Sprinkle the mixture and flaky sea salt on top. Chill for at least one hour until the filling is set.
Prepare the California Raisin Paste ahead of time.
Cut chilled tart using a heated knife.
Serve accompanied with your favourite hot beverage.
Can be made into individual tarts.