STEP 1:
Preheat oven to 350 degrees. Using extra butter, grease the base and side of a 2 liter (8-cup capacity) ovenproof glass bowl (a Pyrex will work). Cut two 2in x 12in strips from baking paper. Line the base and side of bowl with the paper strips so they form a cross, then fill in the gaps with extra baking paper, cutting to fit.

STEP 2:
Beat butter, sugar, and vanilla until light and fluffy. Add eggs, 1 at a time, beating well after each addition. Sift flour over butter mixture. Add milk. Stir until well combined. Divide mixture evenly among 3 bowls. Tint 1 batch bright blue with blue food coloring. Tint second batch pale blue with blue food coloring. Leave third batch plain. Place alternate spoonfuls of the 3 batches into prepared bowl. Using a skewer, swirl together to create a marble effect.

STEP 3:
Bake for 1 hour 15 minutes or until a skewer inserted into the middle comes out clean. Cool cake in bowl for 10 minutes. Turn out onto a wire rack to cool completely.

STEP 4:
Place totally cooled cake on a cake stand or board. Spread thawed truwhip all over cake. If desired, push white chocolate discs, flat-side up, into the frosting to form craters. Top with astronauts. Refrigerate or serve immediately.