Prepare the Cupcakes:
Preheat your oven to 350°F (175°C). Line a 12-cup muffin tin with cupcake liners.

Mix Dry Ingredients:
In a medium bowl, whisk together the flour, sugar, baking powder, and salt.

Combine Wet Ingredients:
In a separate bowl, whisk together the sour cream, water, vegetable oil, egg, and vanilla extract until smooth.

Incorporate Wet and Dry Ingredients:
Add the wet ingredients to the dry ingredients and mix until just combined. Do not overmix.

Fill Cupcake Liners:
Divide the batter evenly among the cupcake liners, filling each about 2/3 full.

Bake:
Bake for 18-20 minutes, or until a toothpick inserted into the center comes out clean.

Cool:
Allow the cupcakes to cool in the tin for 5 minutes, then transfer to a wire rack to cool completely.

Prepare Raspberry Buttercream Frosting:
In a large bowl, beat the melted white chocolate and butter together until creamy. Gradually add the powdered sugar, vanilla extract, and salt, beating until smooth. Add the heavy cream and beat until light and fluffy.

Fill Cupcakes:
Using a small knife or cupcake corer, remove a small portion from the center of each cupcake. Fill the hole with raspberry jam.

Frost Cupcakes:
Pipe or spread the raspberry buttercream frosting onto each cupcake.

Prepare White Chocolate Ganache Drizzle:
In a small saucepan, heat the heavy cream over low heat until warm. Remove from heat and add the white chocolate, stirring until smooth. Allow to cool slightly before drizzling over the frosted cupcakes.

Garnish:
Top each cupcake with a dollop of raspberry jam and a fresh raspberry.