Preheat your oven to 375°F (190°C). In a food processor, pulse together flour, cocoa powder, sugar, and salt. Add cold butter and pulse until mixture resembles coarse crumbs. Drizzle in ice water, 1 tbsp at a time, pulsing until the dough just starts to come together. Press dough evenly into the bottom and up the sides of a 9-inch tart pan. Pierce the bottom with a fork. Bake for 15-18 minutes. Let cool completely.

Combine raspberries, sugar, cornstarch, and lemon juice in a small saucepan. Cook over medium heat, stirring, for 5-7 minutes until thickened. Let cool slightly, then spread evenly in the cooled tart shell.

Place chocolate chips in a heatproof bowl. Heat heavy cream in a saucepan until it just simmers. Pour hot cream over chocolate and let sit for 5 minutes. Whisk gently until smooth and glossy.

Pour the warm ganache over the raspberry layer, spreading evenly. Refrigerate for at least 4 hours, or until the ganache is firm.