Preheat the oven to 400°F. Lightly grease a tart pan; set aside.
In a food processor, pulse together the flour, cocoa, sugar and butter (and salt, if necessary) until the ingredients come together to form a moist dough.
Press the dough firmly into the tart shell, getting it up the sides and between the flutes; create an even layer on the bottom.
Bake the tart shell for 12 minutes. Remove from oven and poke the crust with a fork a few times to release the steam. Use the back of a spoon or measuring cup to firmly press down the crust to form a flatter, even base. Return to oven for 3 minutes more.
Allow tart shell to cool thoroughly. If time is of the essence, place the shell in the freezer to speed the cooling process.
Meanwhile, prepare the ganache.
In a small pot, bring the cream and balsamic to a simmer over medium-low heat, stirring occasionally (don’t let it boil). Place the chocolate in a heat-proof bowl and pour the simmered cream mixture on top.
Whisk to combine the cream and the chocolate. When chocolate is melted, add the butter and continue to whisk until the ganache is glossy and butter is incorporated.
Pour the ganache into a cooled tart shell; gently spread out to an even layer. Allow the tart to sit for 10 minutes to cool.
After the tart has cooled for 10 minutes, place raspberries in even rows on top of the ganache, 4 in each row.
Slice and serve. Store remaining in the fridge, bringing to almost room temperature before serving.