1. Preheat oven to 350℉ (180℃). Grease a 9 x 13 inches (22 x 33 centimeters) baking tin; line the bottom with parchment paper, then grease the parchment and flour the entire tin.
2. In a medium bowl sift together flour, baking powder, baking soda, and salt.
3. In a separate large bowl, using an electric mixer on medium speed, beat butter for 30 seconds. While mixing, slowly rain Redpath® Granulated Sugar into the butter; beat for 5 minutes until light and fluffy. Beat in the eggs and yolks one at a time, allowing each to become fully incorporated before adding the next. Beat in the vanilla.
4. Switch the mixer to low speed and add ¼ of the dry ingredients to the butter mixture; mix until just combined. Add ⅓ of the buttermilk and combine. Alternate adding ¼ of the dry ingredients with ⅓ of the wet, ending with the dry ingredients. Be careful to mix until just combined – do not overmix.
5. Spread cake batter evenly into the prepared pan, using an offset spatula to smooth the top. Bake for 40 minutes or until cake is golden brown and a toothpick inserted in the centre comes out clean. Cool in pan for 15 minutes, then remove to a baking rack to cool completely.
6. Once cake has cooled, use a serrated knife to trim off the domed top of the cake. Cut cake in half to create two 9 x 6.5 inches (22 x 16.5 centimeters) rectangles, then slice each piece horizontally to create 2 layers. Spread bottom layer of each with ½ cup (160 g) of the cherry jam and place the second layer on top. Chill in freezer for 30 minutes.
7. Once chilled, slice each cake into 12 squares, about 2 x 2 inches (5.25 x 5.25 centimeters). Place back in freezer while preparing frosting.