Make the raspberry swirl: In a small saucepan, cook raspberries, 3 tbsp sugar, water, and lemon juice over medium heat for 5-7 mins, mashing often, until thickened. Press through a fine sieve to remove seeds. Let cool completely.

Preheat oven to 350°F (175°C). Ensure oven rack is in lower third. Do not grease a 10-inch tube pan.

Sift cake flour and 3/4 cup (150g) of the superfine sugar together three times into a medium bowl. Set aside.

In a clean stand mixer bowl, whip egg whites, cream of tartar, and salt on medium until foamy. Gradually add remaining 3/4 cup sugar. Add extracts. Whip on high to stiff, glossy peaks.

Sift 1/4 of the flour mixture over meringue. Gently fold with a spatula. Repeat in three more additions until just combined.

Transfer 1/3 of batter to a separate bowl. Drizzle with half the raspberry puree; fold 2-3 times for swirl. Return to main bowl. Top with remaining puree. Fold entire batter 4-5 times for dramatic streaks.

Gently spoon batter into ungreased tube pan. Smooth top. Run a knife through once to marbleize. Tap pan once on counter.

Bake for 35-40 mins, until top is golden and springs back. Immediately invert pan onto its legs or a bottle. Cool completely upside-down, 2-3 hours.

Run a thin knife around edges and center tube. Invert onto a plate to release cake. Slice with a serrated knife and serve.