Combine raspberries, 1 tablespoon sugar, and lemon juice in a small saucepan over medium heat. Cook for 3-4 minutes, stirring and mashing gently, until berries break down and release their juices. Do not boil. Press through a fine-mesh sieve into a bowl, scraping with a spatula to extract all liquid; discard seeds. You should have about 3/4 cup puree. Let cool to room temperature.

Sprinkle gelatin over cold water in a small bowl. Let stand 5 minutes until spongy. Microwave for 10-15 seconds until just melted and liquid, then whisk into the cooled raspberry puree until fully combined.

In a large bowl, beat cold heavy cream with 1 tablespoon sugar until it holds soft peaks - when you lift the beaters, the cream should curl over gently. Do not overwhip. Refrigerate while you prepare the egg whites.

In a clean, dry bowl, beat egg whites with the pinch of salt until foamy. Gradually add remaining 1 tablespoon sugar and continue beating until glossy, stiff peaks form - the whites should hold a firm peak that does not droop when the beaters are lifted.

Gently fold the raspberry-gelatin mixture into the whipped cream until no streaks remain. Then fold in the whipped egg whites in two additions, using a light hand and cutting through the center, scraping the bottom, and turning the bowl. Stop when just combined - a few streaks are fine.

Divide the mousse evenly among 6 ramekins or dessert glasses. Tap gently on the counter to remove large air bubbles. Refrigerate uncovered for at least 2.5 hours, or until fully set and slightly firm to the touch. Serve chilled, topped with fresh raspberries.