Preheat the oven to 350° F (180° C) and line 2 baking sheets with parchment paper or silicone baking mats.
In a large mixing bowl, add the softened butter, melted white chocolate, and salt. Beat using an electric mixer until they are well combined. Mix in the flour, about 1 cup at a time, using your hands to mix once the dough becomes very thick. It should become crumbly, but you should still be able to bring it together into one large mass.
Divide the dough into 24 equal portions. Roll each portion into a ball and place on the baking sheets, then use your thumb to press a well down into the center of each cookie. Bake at 350° F (180° C) for about 8-10 minutes, or until the edges of the cookies become just very slightly browned. If the thumbprints have filled in, use the end of a spoon to press them back down.
Melt the raspberry jam until it is liquefied and smooth. Spoon about 2 teaspoons of jam into each thumbprint. Avoid moving the cookies while the jam is cooling.
After the cookies have cooled for about 30 minutes, melt the white chocolate for the drizzle and spoon it into a pastry bag or plastic bag with the end snipped off to create an opening of about 3-4mm. Pipe the drizzle onto each cookie, then allow the chocolate to cool for a couple of hours before moving. You can store the cookies at room temperature for about 7 days.
