Preheat the oven to 400° F. Butter a 9x13-inch baking pan.
In a large bowl, whisk together the flour, sugar, baking powder, and salt.
Add the cold butter and work it into the flour with your fingertips until small pea-sized pieces remain. Stir in the oil, eggs, heavy cream, and vanilla. Mix just until combined. Gently swirl 1 cup of the strawberry jam through the batter. Do not overmix.
Spoon the batter into the prepared pan. Using a spatula or slightly damp hands, spread the batter evenly.
Bake for 30 to 35 minutes, until the top is golden and a toothpick inserted into the center comes out clean. Let cool completely.
To make the whipped cream, beat the mascarpone and vanilla until smooth. Slowly add the cold heavy cream and continue beating until soft peaks form.
In a bowl, combine the strawberries, lemon juice, and the remaining ½ cup strawberry jam.
Spread the whipped cream evenly over the top. Spoon the strawberry mixture over the whipped cream. Slice and serve + enjoy!
