Cake: Preheat oven to 350 degrees. Butter a 10-inch square pan and line bottom with parchment; butter parchment. Whisk together flours, baking soda, baking powder, and salt.
Beat together butter and sugar with a mixer on medium-high speed until pale and fluffy. Reduce speed to medium. Add whole eggs, 1 at a time, beating until incorporated and scraping down sides of bowl as necessary. Add egg yolks, 1 at a time, and beat until thoroughly combined. Reduce speed to low and gradually add flour mixture in 3 additions, alternating with buttermilk in 2 additions, and beating until combined after each. Beat in vanilla.
Pour batter into pan and spread evenly. Bake, rotating pan halfway through, until cake springs back when lightly touched and a toothpick inserted in center comes out clean, about 50 minutes. Transfer to a wire rack and let cool 10 minutes. Turn out cake onto rack and let cool completely.
Frosting: Meanwhile, combine egg whites, sugar, and salt in a bowl set over a pot of simmering water. Whisk constantly by hand until warm to the touch and sugar is dissolved. (Mixture should feel completely smooth when rubbed between fingertips.)
Turn off heat and remove bowl from stove top. Beat with a mixer, starting on low speed and gradually increasing to medium-high, just until stiff peaks form. Continue beating until fluffy, glossy, and completely cool (test by touching bottom of bowl), about 10 minutes.
With mixer on medium-low speed, add butter, a few tablespoons at a time, beating well after each addition. Beat in vanilla. Reduce speed to low and beat until all air bubbles are eliminated, about 2 minutes. Scrape down sides of bowl with a flexible spatula and continue beating until frosting is completely smooth.
Place cake on a cake plate and trim top with a long serrated knife to level. Spread top and sides with frosting, smoothing and squaring edges. Cut fondant tattoo to a 10-inch square and remove from paper. Carefully apply fondant tattoo, design side up, to cake, starting from a corner and then smoothing the middle.
Serve cake slices with raspberry jam "blood." To get the effect, spoon a thin line of jam along sliced edge of cake. Cake (without fondant tattoo) can be made and frosted 1 day ahead and stored in refrigerator; bring to room temperature before applying fondant tattoo and serving.