Place the freeze-dried raspberries in a food processor and process until you have raspberry dust. Coarsely chop the rosemary sprig.
Combine the chopped rosemary, powdered raspberries, and heavy cream in a medium saucepan and stir to mix everything. Place the pan over medium heat and bring the cream to a simmer, so that bubbles appear all along the sides of the pan. Once it comes to a simmer, take the pan off the heat, cover it with a lid, and let it sit at room temperature for 30 minutes to infuse the cream with flavor.
After 30 minutes, take off the lid and whisk the corn syrup and a pinch of salt into the cream. Return the pan to the heat and bring the cream to a simmer again.
While the cream is heating, place the 10 oz chopped chocolate in a medium bowl. Once the cream simmers, pour the hot cream through a fine mesh strainer over the chopped chocolate, to strain out the rosemary and any stray raspberry chunks.
Let the bowl sit for 1 minute so the hot cream can soften the chocolate, then gently whisk until the chocolate is melted and smooth. Add the butter, and whisk until it melts into the ganache. The ganache should be thick and shiny, like pudding.
Spray an 8" square pan with a light coating of nonstick spray, and line the inside with plastic wrap, pressing as many wrinkles out as possible, and extending the plastic wrap up the sides of the pan. Pour the ganache into the prepared pan and use a small spatula or knife to smooth it into an even layer. Refrigerate the pan for at least 2 hours to firm up the ganache.
Once the ganache is set, remove it from the pan using the cling wrap as handles, and peel the cling wrap off the back. Use a large sharp knife to cut it into small 1-inch squares. If the cuts start looking sloppy, wash the knife in hot water and dry it off between cuts.
If you have the time, set the squares on a baking sheet covered with parchment and let them sit at cool room temperature overnight to develop a slight "skin." This will make it easy to dip them at room temperature. If you don't have the time, you can dip them right away, but dipping cold truffles sometimes causes the outside chocolate coating to crack, so it's preferable to form let the ganache set whenever possible.
When you're ready to dip the truffles, place the chocolate candy coating in a medium microwave-safe bowl, and microwave in 30-second increments, stirring after every 30 seconds, until melted and smooth. Let the coating cool down until it is warm and fluid but not hot to the touch.
Make sure the chocolate texture sheet is clean and dry, and place it face-up on a baking sheet. Using dipping tools or a fork, dip a truffle square into the melted candy coating, submerging it completely. Bring it up out of the chocolate and let the excess drip back into the bowl, then gently scrape the bottom of the truffle against the lip of the bowl to remove excess chocolate.
Flip the truffle upside-down onto the texture sheet, so that the top of the truffle is on the bottom and the dipping tools are on the top. Pull the dipping tool away from the truffle and leave it on the texture sheet to set completely. Repeat until all of the truffles are dipped and placed on the sheet. (If they won't all fit, do them in batches.) Refrigerate the tray to set the coating completely, for about 20-30 minutes.
Once the coating is very hard and shiny, peel the chocolates off the texture sheet. If desired, use a dry brush to lightly brush the tops with luster dust. For the best taste and texture, serve the truffles at room temperature.