Strawberry Jam:

1. In a small pot, combine strawberries, granulated sugar, and water.
2. Cook over medium-high heat, stirring occasionally until it boils.
3. Continue cooking until the mixture thickens to a jammy consistency.
4. Transfer to a bowl and cool completely in the fridge.

Chocolate Cake:

1. Preheat oven to 350°F (175°C). Line the bottom of two 6-inch round cake pans with parchment paper.
2. In a medium bowl, whisk together flour, cocoa powder, baking powder, baking soda, and salt. Set aside.
3. In a large bowl, whisk melted butter, oil, granulated sugar, and brown sugar until combined.
4. Add eggs one at a time, mixing well after each.
5. Gradually add half of the flour mixture and then half of the milk, mixing until just combined.
6. Divide the batter evenly between the pans. Smooth the surface.
7. Bake for 40-45 minutes or until a toothpick comes out with a few crumbs.
8. Let the cakes cool in the pans for 10 minutes, then turn them out onto a wire rack to cool completely.

Strawberry Cream Cheese Frosting:

1. In a large bowl, beat softened butter until creamy.
2. Add cream cheese and beat until smooth.
3. Add powdered sugar and beat on low until combined.
4. Add strawberry jam and vanilla extract, then beat until smooth.
5. Transfer a portion of the frosting to a piping bag.

Assembly:

1. Use a serrated knife to level the cakes and cut them in half horizontally to create four layers.
2. Place the first layer on a cake turntable. Pipe a ring of frosting around the edge.
3. Spread about 4 tablespoons of strawberry jam inside the frosting ring, then sprinkle with diced strawberries.
4. Repeat for the remaining layers, finishing with frosting on top.
5. Decorate with halved strawberries on top.