Make the yellow cake mix: Put both the flours in a food processor. Add sugar, baking powder, salt and pulse until combined. Cut butter into smaller pieces and add to the flour mixture. Process until well combined. Use the mix immediately or refrigerate in an airtight container for up to a month.
Make the Cake: Preheat oven to 350°F. Lightly grease a 8" round baking pan.
Take half of the cake mix from above (it came to about slightly less than 2½cups), add the egg, milk and vanilla. Beat with a electric mixer for 1 minutes on low speed. Increase the speed to medium-high and beat for another 2 minutes. Transfer to the prepared pan and bake for 30-35 minutes or until a toothpick inserted in the middle comes out clean.
Let the cake cool slightly in the pan. Carefully slip the cake onto a wire rack and cool completely.
Make the Mascarpone Filling: Add the yolks and sugar in a small bowl and whisk until pale and light in color. Bring some water to a boil in a medium saucepan; lower the heat and let the water simmer very lightly. Place the bowl with the yolks on the saucepan (make sure the bowl does not touch the water) and whisk continuously until the mixture starts to thicken and bubbles start to form around the edges, takes about 15-20 minutes. Set aside to cool.
Beat cold heavy cream until stiff peaks form.
Beat softened mascarpone and stir into the egg mixture until combined.
Gently fold in whipped heavy cream into the above mixture. Refrigerate until ready to use.
Make the espresso syrup: Add sugar to espresso and bring to a boil. Remove from heat and set aside to cool.
Assemble the Cake: When the cake is completely cooled, split it into 2 pieces. Place the bottom piece in a 8" spring form pan. Sprinkle half the espresso syrup on the cake. Spread with half the filling and top with the other layer. Sprinkle with the remaining espresso syrup and spread the frosting.
Chill the cake for at least 4-6 hours before serving.