Process the brownie ingredients. Add the walnuts to a food processor bowl fitted with an S blade and process until the nuts are coarsely ground. Be careful not to over-process the nuts; they should retain some texture. Add the dates, cocoa powder, hemp hearts, and salt to the food processor and process until all the ingredients begin to stick together. You might be tempted to add more dates because the brownie mixture will be tender and slightly crumbly at first, but "crumbly is exactly what you want as long as the mixture sticks together when you press it between your fingers. If the mixture is too dry, pulse it a little bit more. Finally, add the chopped walnuts to the food processor and pulse until just combined
Press the mixture into a pan. Transfer the mixture to a parchment paper-lined baking dish (I used a 6.5" x 6.5"/16.5 cm x 16.5 cm glass container) and press it into a smooth, even layer.
Mix the chocolate ganache ingredients. Add the coconut oil, cocoa powder, maple syrup, and coconut cream to a medium bowl and whisk until smooth.
Assemble the brownies. Pour the chocolate ganache on top of the brownies and spread it evenly. Tap out any air bubbles.
Chill. Transfer the brownies to the refrigerator to firm up, for about 1 hour. Once firm to the touch, remove the brownies from the baking dish (by lifting the parchment paper) and cut them into squares. To cut the brownies cleanly, run a sharp knife under hot water for about 20 seconds, wipe off excess water, and press the knife down slowly, making the first cut. Run the knife under hot water again to reheat it. Wipe the blade clean, then make the second cut. Repeat until all the brownies are cut.
Store. Leftover brownies keep well in an airtight container in the refrigerator for up to 2 weeks. For longer-term storage, freeze in an airtight container for up to 3 months. The freezer will produce condensation on the chocolate if the brownies are brought to room temperature straight from the freezer. So, for best results, transfer the frozen brownies to the refrigerator 24 hours before serving.