In an 8-inch square glass baking dish, place the butter and chocolate and microwave on high until melted, about 2 minutes. Remove the dish from the oven and whisk to combine. (The chocolate may hold its shape after being microwaved, but really is melted; simply whisk to incorporate into the melted butter.)
Add the sugar and stir well to combine. Sift the flour and salt into the chocolate mixture and add the eggs, whisking until smooth, scraping around the sides to incorporate all the ingredients. Add the vanilla and whisk to combine. Stir in the chocolate chips and microwave on high until set and a cake tester or toothpick inserted into the center comes out clean, 4 1/2 to 5 minutes.
NOTE: Cooking times may vary, depending upon the strength of the microwave.
Remove from the oven and let cool on the countertop for 15 minutes before serving.
Yield: about 8 servings
Sweetened Whipped Cream:
Place the cream in a medium bowl and beat with an electric mixer at medium speed or by hand until it becomes thick and frothy. While beating, add the sugar and vanilla and continue to beat until soft peaks form, being careful not to over-mix. Serve immediately.
Yield: 2 cups