a 6- to 7-inch plastic chocolate dome mold; a 12-inch silver cake board; a cake turntable
For the cake: Preheat the oven to 325 degrees F. Spray two 9-inch round cake pans with nonstick cooking spray.
Whisk the flours, cinnamon, baking powder and salt together in a large bowl and set aside.
Cream the butter and sugar together in a stand mixer until light and fluffy. Add the eggs one at a time until just combined, then add the vanilla. Combine the milk and rum in a measuring cup, then alternate adding the dry ingredients and milk mixture to the butter mixture in two additions each. Beat until combined.
Pour the batter into the prepared cake pans and bake until a toothpick inserted in the center of a cake comes out clean, 30 to 35 minutes. Let cool on a wire rack until cool enough to handle, then turn the cakes out onto the wire rack to cool completely.
For the decoration: Meanwhile, put the white melting candies and coconut oil in a medium heatproof glass or metal bowl that fits over a small saucepan without touching the bottom. Fill the saucepan with a couple of inches of water and place over medium heat. Place the bowl of white melts over the top and melt until smooth.
Pour a small amount of the white chocolate into a 6- to 7-inch plastic chocolate dome mold and swirl the mold to coat the inside completely in a thin layer. Place in the refrigerator for 1 minute. Remove and spoon 1/4 cup more white chocolate into the mold. Using the back of the spoon, smooth the white chocolate all around the inside to create a thicker layer; refrigerate for 1 to 2 minutes. Repeat this process 2 more times, so that you have a solid white chocolate layer in the mold. Leave in the refrigerator while you finish assembling the cake. Place any leftover melted chocolate in a disposable pastry bag or resealable plastic bag.
To make the penguins, form a ball of black gum paste about the size of a golf ball. Using the insides of your palms or the tabletop, gently roll one end to form the ball into a egg shape. Orienting the pointier side of the egg up, make a small snip with a sharp pair of scissors on one side of the egg, close to the bottom, and use your finger to lift the snip up to form a wing. Repeat directly across from this snip on the other side to make the second wing. Repeat the making egg shapes and snips 3 times for 3 more penguins.
Take a small amount of white gum paste and roll it out thinly, dusting with cornstarch so it doesn't stick to your surface. Cut out 4 small teardrops with a cutter or very sharp paring knife. Trim a small V-shaped notch from the tip of each white teardrop. Brush a small amount of vodka on one side of a white shape and adhere to the front of a black penguin body. Repeat with the remaining penguins.
Split the orange melting candies in half, then gently press the body of the penguin onto 2 of the orange melt halves to position them for feet. Lift the penguin off and brush the foot indents with vodka, then press the penguin gently back on top of the orange melts to adhere. Repeat with the remaining penguins. Cut the sour belts in half lengthwise, then cut into 6-inch strips. Tie one in a loose knot and drape around a penguin's head; tighten as needed, then trim to the desired length. Repeat with the remaining penguins. Press an orange chocolate-covered sunflower seed into each head to create a beak on each penguin. Use edible markers to draw eyes on each.
Level both cake layers using a serrated knife. Flip one round upside down and secure to a 12-inch round silver cake board set on a cake turntable with a dollop of Frosting. Spread an even layer of Frosting (about 1/2 cup) over the top of the cake layer. Flip the second cake layer upside down and place atop the Frosting. Frost the entire cake with a thin even coat of Frosting. If your Frosting has picked up a lot of crumbs, refrigerate the cake 30 minutes. Generously frost the cake with a second layer of Frosting, using an offset spatula to create swirls and snow drifts.
Remove the chocolate mold from the refrigerator and invert onto a clean work surface, using the edges of the mold to lift it off. Use a sharp paring knife to cut a broken-looking hole into the front of the igloo. Place the chocolate dome on top of the cake, positioning it close to one edge. Snip a very small bit of the tip off the end of the pastry bag with the white chocolate. Create 'ice bricks' on the igloo by piping horizontal lines at 1-inch intervals around the dome (put the pastry bag back in the microwave for a couple of seconds if it gets too hard to pipe). Then pipe in staggered vertical lines to create the bricks.
Add more Frosting where you wish to make snow drifts against the igloo and around the bottom of the cake. Place your penguins on top and along the sides of cake.
Country Bling 7-Minute Frosting:
Place the sugar and 3/4 cup water in a saucepan and stir until dissolved. Bring to a boil over medium heat.
Meanwhile, put the egg whites, cream of tartar and salt in the bowl of a stand mixer fitted with a whisk attachment and beat to stiff peaks. With the mixer on low, stream in the boiled sugar syrup, then add the vanilla and turn the mixer to high. Beat for 7 minutes.