Pour 1 cup of the cream into a 4-cup glass measure; bring to a simmer in microwave, about 2 minutes; add white chocolate. Let stand 2 minutes. Whisk until smooth; refrigerate while making cake.Heat the oven to 350°F. Line bottom of two 8 x 2-in. round cake pans with parchment or wax paper; coat pans and paper with nonstick cooking spray.In a medium bowl, whisk together flour, baking powder, poppy seeds and salt. Beat sugar, butter, lemon zest and juice with mixer at medium speed until light and fluffy, about 3 minutes. Beat in egg whites and whole egg until smooth. With mixer on low, alternately beat in flour mixture and milk until incorporated. Continue to beat batter on medium speed for 3 minutes. Divide batter between prepared pans and smooth tops with spatula.Bake for 35 to 40 minutes, until a wooden pick inserted in the centers comes out clean. Cool in pans on wire rack 10 minutes. Loosen edge of cakes with knife; invert onto the rack and remove parchment paper. Turn cakes right side up. Cool completely.In large bowl, beat chilled white-chocolate mixture with remaining 1 1⁄2 cups cold cream until stiff peaks form.With a serrated knife, halve cakes horizontally. Place 1 layer on a serving plate, cut side up; spread with 2 Tbsp of the jam. Spread a scant 2⁄3 cup frosting over jam. Arrange one third of the sliced strawberries evenly over frosting. Top with a second cake layer; spread with another 2 Tbsp jam, frosting and a layer of berries. Repeat with a third layer. Brush the cut side of remaining cake layer with remaining jam and place jam-side down on top. Cover cake with remaining frosting.