Prepare the Sponge Cake

1. Preheat the Oven: Preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper.
2. Whisk Eggs and Sugar: In a mixing bowl, whisk the eggs and sugar together until the mixture becomes light and fluffy. This should take about 5-7 minutes.
3. Fold in Flour and Vanilla: Gently fold in the flour, vanilla extract, and a pinch of salt. Be careful not to deflate the batter.
4. Bake: Pour the batter into the prepared baking sheet and bake for about 8-10 minutes or until the cake is golden and springy to the touch. Let the cake cool completely.
5. Cut the Cake: Once cooled, cut the sponge cake into a circle or square that fits your entremets mold (usually around 6-8 inches in diameter).

Prepare the Pistachio Mousse

1. Soak Gelatin: Soak the gelatin sheets in cold water for about 5 minutes. If using powdered gelatin, sprinkle it over 2 tablespoons of cold water and let it bloom.
2. Heat Milk, Pistachio Paste, and Sugar: In a saucepan, combine the milk, pistachio paste, and sugar. Warm the mixture over medium heat until the sugar dissolves.
3. Add Gelatin: Remove from heat, then add the bloomed gelatin to the mixture. Stir until fully dissolved.
4. Cool the Mixture: Let the pistachio mixture cool to room temperature.
5. Whip Cream: Whip the heavy cream to soft peaks.
6. Combine: Gently fold the whipped cream into the pistachio mixture until smooth and well combined.

Prepare the Vanilla Cream

1. Soak Gelatin: Soak the gelatin in cold water for about 5 minutes.
2. Cook the Milk and Egg Yolks: In a saucepan, heat the milk and vanilla extract. In a separate bowl, whisk the egg yolks and sugar together. Gradually pour the hot milk into the egg mixture while whisking constantly to temper the eggs.
3. Thicken the Custard: Return the mixture to the saucepan and cook over low heat, stirring constantly, until it thickens and coats the back of a spoon. Remove from heat.
4. Add Gelatin: Stir the bloomed gelatin into the custard until fully dissolved. Let it cool to room temperature.
5. Whip the Cream: Whip the heavy cream to soft peaks.
6. Combine: Once the custard has cooled, fold in the whipped cream gently until smooth.

Assemble the Entremets

1. Prepare the Mold: Line an entremets ring (or a cake ring) with acetate strips for easy removal. Place the sponge cake at the bottom of the mold.
2. Layer the Pistachio Mousse: Pour a layer of pistachio mousse over the sponge cake, smoothing it evenly. Freeze the entremets for about 30 minutes to set the mousse.
3. Layer the Vanilla Cream: Once the pistachio mousse has set, pour a layer of vanilla cream over it. Return the entremets to the freezer for another 1-2 hours to fully set.
4. Final Pistachio Mousse Layer: After the vanilla cream layer is set, add the remaining pistachio mousse, smoothing it out evenly. Freeze the entremets for at least 4 hours or overnight for best results.

Prepare the Glaze

1. Melt White Chocolate: In a heatproof bowl, melt the white chocolate and heavy cream together over a double boiler or in the microwave, stirring every 20 seconds until smooth.
2. Add Pistachio Paste: Stir in the pistachio paste and a small amount of green food coloring, if desired. Let the glaze cool slightly before using.

Glaze the Entremets

1. Unmold the Entremets: Once the entremets has set, carefully remove the ring and acetate.
2. Pour the Glaze: Pour the pistachio glaze over the entremets, allowing it to drip down the sides for a beautiful, glossy finish.
3. Chill: Refrigerate the entremets for at least 30 minutes to set the glaze.

Decorate the Entremets

1. Garnish: Decorate with crushed pistachios, fresh berries, or edible flowers for a touch of color and elegance.