Preheat the oven to 180°C (355°F). Line two 6-inch round cake pans with parchment paper.
Add dry ingredients to a large bowl and whisk until well combined.
Add wet ingredients and mix until just combined. Gently fold in raspberries.
Divide the batter between the prepared pans. Tap pans to remove air bubbles.
Bake for 43-48 minutes, or until a toothpick comes out clean. Let cool in pans for 10 minutes, then transfer to a cooling rack.
For the jam: Combine raspberries, sugar, and a splash of water in a saucepan. Cook for 5 minutes, mash berries, then add cornstarch slurry to thicken. Set aside.
For the frosting: Whip vegan butter until light and fluffy. Gradually add powdered sugar and color. Whip until smooth.
Assemble the cake: Trim domed cake layers. Place the first layer on a serving plate. Add frosting, jam if desired, and the second layer. Crumb coat and chill for 20 minutes.
Frost the cake with a thicker layer, smoothing with a spatula. Pipe decorations and top with fresh berries.