Happy Purrthday Cake

softened, for greasing

or plant-based milk

or other neutral-tasting oil

to make gluten-free, substitute with a gluten-free self-raising flour blend that contains added xanthan gum, plus 1/2 tsp xanthan gum

or granulated

or muscovado

or use gluten-free baking powder

or granulated

use just the thick part on top

to taste

at room temperature, cubed, or vegan butter - use one that's close to 80% fat content

or plant-based milk

this is added to a third of the buttercream, omit this if making the recipe gluten-free