To prepare brownies, butter a 9-by-9-inch pan, and then add a layer of parchment paper, leaving the edges long enough to lift the brownies from the pan once cool for easier slicing. Butter the parchment paper, pressing it to adhere smoothly to the pan.
Melt butter in a small saucepan over medium heat. Add sugar and stir to combine. Continue to cook until the mixture is hot but not bubbling; it will become shiny as you stir it. Transfer mixture to the bowl of a standing electric mixer. Stir in cocoa, salt, baking powder, and vanilla. Add the eggs, one at a time, beating until smooth. Add flour, stirring until well combined.
Scrape the batter into the prepared pan, spreading it as evenly as you can.
Bake for 20 to 25 minutes in an oven preheated to 350°F, until a toothpick inserted in the center comes out clean. Remove from the oven and cool to room temperature on a rack.
While the brownies bake, prepare the cookie dough filling. Beat butter, sugars, and salt on medium speed in the bowl of a standing electric mixer until light and fluffy. Add vanilla and cream and mix well. Add flour and mix on low speed until incorporated. Stir in chocolate chips by hand.
Immediately shape the dough into scant 1-inch balls (about 2 teaspoons each). Arrange dough balls on a baking sheet lined with parchment paper. Freeze the dough while the brownies cool (if making in stages, make sure you freeze the cookie dough balls for at least an hour).
To assemble, cut brownies into 1-inch squares. Squish the brownies and press them around the cookie dough balls, adding more brownie if necessary to create an even coating around each ball. Place brownie coated balls in the freezer while you prepare the chocolate coating.
Melt chocolate in a bowl set over simmering water (even if you have a double boiler, a bowl's sloped sides work better for dipping), stirring frequently until the chocolate is smooth and liquid.
Working one at a time, set cookie balls on the flat surface a fork (not speared!) and dip them into the chocolate, coating each one completely. Tap the fork on side of the bowl to remove excess chocolate before returning balls to to the lined baking sheets. Sprinkle each bonbon with sea salt just after dipping, if desired.
Chill chocolate-dipped balls until set. Store, chilled, in an airtight container for up to 1 week.