1. Prepare the Raspberry Insert (Start Ahead):

• In a small bowl, sprinkle the 1 tsp gelatin over the 1 tbsp cold water. Let bloom for 5-10 minutes.
• Combine raspberries, 2 tbsp sugar, and lemon juice in a small saucepan. Cook over medium heat, stirring occasionally, until raspberries break down and the mixture simmers (about 5-8 minutes).
• Strain the mixture through a fine-mesh sieve into a clean bowl, pressing gently on the solids to extract maximum puree. Discard seeds/solids.
• Return the smooth puree to the saucepan. Add the bloomed gelatin and stir over low heat until the gelatin is completely dissolved (do not boil).
• Pour the raspberry mixture into the smaller silicone mold.
• Freeze until completely solid (at least 2-3 hours).

2. Prepare the Sponge Cake Base:

• Preheat oven to 350°F (175°C). Line a small baking sheet (like a quarter sheet pan) with parchment paper.
• In a mixing bowl, beat the egg and 3 tbsp sugar with an electric mixer on high speed until pale, thick, and tripled in volume (ribbon stage – about 5 minutes).
• In a separate small bowl, whisk together the flour, baking powder, and salt.
• Gently fold the dry ingredients into the egg mixture in two additions, being careful not to deflate the batter.
• Stir in the milk and vanilla extract until just combined.
• Spread the batter thinly and evenly onto the prepared parchment-lined baking sheet (aim for a rectangle large enough to cut your base circle from).
• Bake for 10-15 minutes, or until the sponge is lightly golden and springs back when gently touched.
• Let the sponge cool completely on the baking sheet on a wire rack.
• Once cool, use a round cookie cutter (slightly smaller than the diameter of your large dome mold) to cut out a circle of sponge cake. Set aside.

3. Prepare the Matcha Mousse:

• Place the finely chopped white chocolate in a medium heatproof bowl.
• Heat ½ cup (120ml) of the heavy cream in a small saucepan until it just begins to simmer around the edges. Pour the hot cream over the white chocolate. Let sit for 2-3 minutes, then whisk gently until smooth and melted. Set aside to cool slightly.
• In a small bowl, sprinkle the 1 ½ tsp gelatin over the 2 tbsp cold water. Let bloom for 5-10 minutes.
• In another small bowl, whisk the matcha powder with the 2 tbsp hot water until smooth and no lumps remain, forming a paste.
• Add the bloomed gelatin to the slightly warm white chocolate mixture and whisk until fully dissolved.
• Whisk the matcha paste into the white chocolate mixture until well combined and uniform in color. Add the pinch of salt and optional sugar if desired (taste first). Let this mixture cool to room temperature (important!).
• In a separate, chilled bowl, whip the remaining ½ cup (120ml) cold heavy cream with an electric mixer until soft peaks form.
• Gently fold the whipped cream into the cooled matcha-white chocolate mixture in two additions until just combined and no streaks remain. Be careful not to overmix.

4. Assemble the Dome Cake:

• Ensure your large dome mold is clean and dry.
• Pour about half to two-thirds of the matcha mousse into the large dome mold. Use a small spatula or spoon to spread the mousse up the sides of the mold, ensuring there are no air pockets, especially at the bottom (which will be the top).
• Carefully unmold the frozen raspberry insert. Gently press it into the center of the matcha mousse in the large dome mold.
• Pour the remaining matcha mousse over and around the raspberry insert, filling the mold almost to the top, leaving just enough space for the sponge cake base. Smooth the top of the mousse.
• Place the cut sponge cake circle on top of the mousse, pressing gently so it adheres and is level with the top edge of the mold.
• Cover the mold tightly with plastic wrap.
• Freeze the entire dome cake until completely solid (at least 6 hours, but preferably overnight). This is crucial for clean unmolding.

5. Unmold and Garnish:

• Once frozen solid, carefully peel the silicone mold away from the frozen matcha raspberry dome cake. Place the dome (sponge side down) onto a serving plate or cardboard cake round.
• Let the cake thaw slightly in the refrigerator for at least 30-60 minutes before garnishing and serving (this allows it to soften slightly for better texture but remain firm).
• Garnish as desired: Drizzle with melted and slightly cooled white chocolate, sprinkle with matcha powder or powdered sugar, and/or arrange fresh raspberries around the base or on top.

6. Serve:

• Slice the Matcha Raspberry Dome Cake using a sharp knife dipped in hot water and wiped clean between cuts for neat slices that reveal the beautiful layers inside.
• Serve chilled. Leftovers should be stored covered in the refrigerator.