Prepare the Roasted Strawberries:

1. Preheat your oven to 350°F (175°C).
2. Toss the strawberries with the granulated sugar and spread them on a baking sheet.
3. Roast for about 40 minutes, or until soft and syrupy.
4. Let cool completely.

Make the Berry Jam:

1. In a medium saucepan, combine the mixed berries, granulated sugar, and lemon juice.
2. Cook over medium heat until the berries break down and the mixture thickens, about 10 minutes.
3. Stir in the cornstarch mixture and cook for another 1-2 minutes until thickened.
4. Let cool completely.

Prepare the Biscoff Sponge:

1. Preheat your oven to 350°F (175°C).
2. Grease and line three 8-inch round cake pans with parchment paper.
3. In a large bowl, whisk together the flour, granulated sugar, light brown sugar, baking powder, baking soda, and salt.
4. In another bowl, mix the applesauce, plant-based milk, melted coconut oil, vanilla extract, and Biscoff spread until smooth.
5. Add the wet ingredients to the dry ingredients, mixing until just combined.
6. Fold in the ground pistachios.
7. Divide the batter evenly among the prepared pans.
8. Bake for 25-30 minutes, or until a toothpick inserted into the center comes out clean.
9. Allow the cakes to cool in the pans for 10 minutes, then transfer to a wire rack to cool completely.

Prepare the Biscoff Buttercream:

1. In a large bowl, beat the dairy-free butter and Biscoff spread until creamy.
2. Gradually add the powdered sugar, mixing until smooth.
3. Add plant-based milk as needed to achieve a spreadable consistency.

Prepare the Biscoff Drip:

1. Melt the Biscoff spread with the coconut oil or dairy-free butter until smooth and slightly runny.

Assemble the Cake:

1. Place one cake layer on a serving plate.
2. Spread a layer of berry jam over the cake layer.
3. Pipe or spread a layer of Biscoff buttercream over the jam.
4. Add some roasted strawberries on top.
5. Repeat with the remaining layers, finishing with a layer of Biscoff buttercream on top.

Add the Drip and Toppings:

1. Pour the Biscoff drip over the top edge of the cake, allowing it to drip down the sides.
2. Sprinkle with crushed Biscoff biscuits.
3. Dust with powdered sugar if desired.

Serve:

1. Slice and enjoy this beautiful summer cake!