Lemongrass Milk:

Cut lemongrass into 1/4" slices. Put into small saucepan with milk. Bring just almost to a boil then reduce heat and simmer for four minutes. As soon as milk heats begin to stir frequently to prevent milk from burning. Remove saucepan from heat and steep for 10 minutes. Strain milk into a measuring cup. Top up with more milk if needed to have 2/3 cup lemongrass milk. Discard lemongrass.

Lemongrass Cake:

Grease two 6" cake pans with butter. Cover the bottom with a cut out circle of parchment paper and flour the sides. Preheat oven to 350.°

In medium bowl, whisk together flour, baking powder, and salt. Set aside.

In stand mixer with a paddle attachment (this recipe can also be made by hand), cream the butter and sugar together on medium-high for about 3 minutes until pale and fluffy.

Reduce speed and mix in eggs, one at a time, followed by vanilla. Next, alternate additions of dry ingredients and lemongrass milk (dry-milk-dry-milk-dry). Be sure everything is well incorporated between each addition. Finally, mix in the lemongrass paste.

Pour batter evenly into the prepared cake pans. Weigh with a scale for most accurate evenness. Bake for approx. 35 minutes, checking doneness by inserting toothpick in center. It should come out almost clean. Be careful not to over bake as you would lose some of the lemongrass flavour. Cool cakes in pans for 10 minutes, then cool the rest of the way on wire rack. Make sure to cool completely before decorating.

Key Lime Frosting:

In stand mixer with paddle attachment on medium speed, mix butter, zest, and vanilla together until creamy. Add 1/3 of icing sugar. Add 1 tbsp lime juice. Add 1/3 icing sugar. Add 1 tbsp lime juice. Add final 1/3 icing sugar. Add 1 tbsp milk (you can add more milk to adjust consistency if desired). This frosting recipe makes enough for a fairly thin layer on this cake. If you like lots of frosting, I recommend doubling it.