Step 1: Preheat your oven to 180°C (350°F) and grease and line two 8-inch round cake pans with parchment paper.
Step 2: In a large bowl, cream together the softened butter and caster sugar until light and fluffy, usually about 5 minutes.
Step 3: Beat in the eggs one at a time, ensuring each is fully incorporated before adding the next. Stir in the orange zest and juice.
Step 4: Sift together the flour, baking powder, and salt. Gently fold the dry ingredients and the ground pistachios into the wet mixture until just combined.
Step 5: Divide the batter evenly between the prepared pans and smooth the tops. Bake for 30-35 minutes or until a skewer inserted into the center comes out clean.
Step 6: Allow the cakes to cool in the pans for 10 minutes before transferring to a wire rack to cool completely.
Step 7: To make the buttercream, beat the butter until pale and smooth. Gradually add the powdered sugar and the bloomed saffron milk, beating until light and airy.
Step 8: Spread a layer of buttercream on one cake layer, place the second layer on top, and frost the top and sides of the cake. Garnish with crushed pistachios.