Slice the vanilla bean in half and add to a baking dish along with the fruit, sugar, and lemon juice. Toss gently to combine.
Roast for 15 minutes, then stir and roast for another 10-15 minutes until the berries are soft and syrupy.
Remove from the oven and let cool fully to room temperature.
Store in an airtight container in the fridge for up to a week!
Vanilla Sheet Cake
Preheat oven to 350°F and line a 9x13 inch cake pan with parchment paper.
In a large bowl, whisk together the melted butter and sugar until smooth. Add in the eggs and vanilla and whisk until fully incorporated.
In a separate bowl, sift together the flour, baking powder, and salt.
Mix half of the dry ingredients into the sugar mixture, then add in the milk. Once incorporated, add in the remaining dry ingredients and mix until just combined.
Pour the batter into the lined cake pan and smooth into an even layer.
Bake at 350°F for 25-35 minutes or until a cake tester inserted near the center comes out clean.
Remove from the oven and let cool completely to room temperature.
Lemon Frosting
In a large bowl using a handheld mixer (or stand mixer fitted with paddle attachment), cream together the room temperature butter and powdered sugar until smooth.
Add in the lemon juice and beat frosting on high for 4-5 minutes until light and fluffy.
If needed, add in milk 1 tablespoon at a time until desired consistency is reached.
Assembly
Use the end of a round wooded spoon or chopstick to poke small holes in the surface of the cake.
Spoon a thin layer of cooled roasted berries and the leftover juices, over the top of the cake and let sit for about 20 minutes to absorb.
Spoon dollops of frosting over the surface of the cake, then gently smooth into an even layer, using an offset spatula to make big swirls in the frosting.
Decorate the cake with fresh berries and flowers if desired!
This cake is best eaten the same day! Store the cake in the fridge for up to 4 days. However, it will taste best when served at room temperature! I like to let it sit at room temperature for about an hour before serving.
Notes
For a lighter, less sweet frosting: Use 8 ounces of mascarpone cheese and ½ cup unsalted butter.