Place a rack in the center of the oven, and preheat the oven to 350°F.
Generously butter and flour a 10" tube pan, and shake out the excess flour.
Set the pan aside.
For the molasses batter, place the butter and sugar in a large mixing bowl, and beat with an electric mixer on medium speed until fluffy and lighter in color, about 3 minutes.
Beat in the egg yolks, one at a time, just until combined.
Scrape down the sides of the bowl with a rubber spatula.
Beat in the molasses on medium speed just until combined.
Place the flour, soda, cream of tartar, cinnamon, mace, nutmeg, and cloves in a small bowl and sift together.
Add to the batter in 3 additions, alternately with the buttermilk in 2 additions.
Beat on medium speed, just until each is combined.
Scrape the bowl often and set aside.
For the lemon batter, place the butter, sugar, and lemon zest in a large mixing bowl, and beat on medium speed until fluffy and lighter in color, about 3 minutes.
Scrape down the sides of the bowl and add the lemon juice.
Beat just until combined.
Place the flour, soda, and cream of tartar in a small bowl and sift together.
Add to the batter in 3 additions, alternately with the buttermilk in 2 additions, beating on medium speed just until each is combined.
Scrape the bowl often and set aside.
Beat the egg whites and salt in a clean medium-size bowl with clean beaters on high speed until soft peaks form, 3 to 4 minutes.
With the spatula, gently fold about a quarter of the whites into the lemon batter, just until combined.
Fold in the remaining whites, just until combined.
Dollop the batters into the bottom of the prepared pan, alternating each flavor 3 times.
Gently rap the pan once against the countertop to settle the batters.
With a butter knife, swirl the batter together a couple of times, but don’t overdo it.
Place the pan in the oven.
Bake until the cake is golden brown and a toothpick inserted near the center emerges clean, 50 to 55 minutes.
Cool the cake in the pan on a wire rack for 10 to 15 minutes.
Run the tip of the knife around the cake to loosen it from the sides and tube; invert once and then again so the cake is right side up on the rack.
Cool completely, 1 hour.
If desired, serve with the modern Lemon Glaze.
Slice and serve.
Notes / Tips / Wine Advice:
If you want to use a Bundt pan, the baking time will be 42 to 47 minutes.
LEMON GLAZE:
Whisk together 1½ cups confectioners’ sugar and 2 to 3 tablespoons fresh lemon juice until smooth. Poke holes in the top of the cooled cake with a fork, and spoon the glaze over the top of the cake.