01 - Combine flour, powdered sugar, and salt in a mixing bowl. Incorporate cold butter with fingertips until mixture resembles coarse breadcrumbs. Add egg yolk and 1 tablespoon cold water, stirring until dough just forms; add additional water if necessary.
02 - Shape dough into a disc, wrap in plastic wrap, and refrigerate for 30 minutes.
03 - Preheat oven to 350°F. Roll out dough on a lightly floured surface to fit a 9-inch tart pan. Press dough into pan and trim excess. Prick base with a fork.
04 - Line dough with parchment paper and fill with pie weights or dried beans. Bake for 15 minutes, remove weights and parchment, then bake an additional 7 to 10 minutes until lightly golden. Allow to cool completely.
05 - Heat heavy cream in a saucepan until just simmering. Pour over chopped chocolate in a bowl and let stand for 1 minute. Stir gently until smooth, then incorporate softened butter until glossy.
06 - Pour ganache into cooled pastry shell, smoothing the surface. Allow to rest at room temperature for 10 minutes.
07 - Arrange fresh raspberries evenly over ganache. For a shiny finish, warm raspberry jam with water and brush lightly over berries.
08 - Refrigerate tart for at least 30 minutes prior to slicing and serving.