Preheat the oven to 350°F (175°C). Line an 8-inch square baking pan with parchment paper so that the paper overhangs on two opposite sides. Grease the paper and any exposed parts of the inside of the pan.
Place the butter and chocolate in a large microwave-safe bowl. Heat in the microwave at half-power in 30-second increments until the butter has melted and the chocolate melts when stirred. Set aside to cool slightly.
Whisk together the flour, cocoa powder, and salt . Set aside.
Place the sugar, eggs, and vanilla in a mixing bowl, and mix well.
Add the sugar mixture to the chocolate mixture, and mix well. Then add the flour mixture, and mix until combined.
Stir in the chopped strawberries.
Transfer the batter to the prepared pan, and spread evenly. Dollop the jam over the top of the batter, and use a thin knife to swirl into the brownies. If you like, place more strawberries on top of the batter.
Bake for 35 to 40 minutes, or until a pick inserted into the center comes out with a few crumbs.
Place the pan on a wire rack, and allow the brownies to cool completely. Use the overhanging lining to lift the brownies out of the pan and onto a cutting board to cut into squares. (These are fudgy, gooey brownies, so you may want to refrigerate the brownies briefly before cutting them.)
Notes
*You'll need 4 or 5 medium strawberries. If you want to add a few slices or chopped berries on top of the brownies before baking, you'll need another 1 or 2 strawberries.
Store in an airtight container in the refrigerator up to 5 days.