Pre‑heat oven to 350 °F (175 °C). Grease and flour two 8‑inch (or 9‑inch) round pans.

In mixer bowl: combine flour, sugar, salt and baking powder. Mix ~30 seconds.

In separate bowl: whisk eggs, orange juice concentrate, milk and orange extract (or zest + vanilla).

With mixer on low, add butter pieces to dry ingredients a few at a time until crumbly. Increase to medium; beat ~1½ minutes until smooth. Scrape bowl.

Add half the egg/milk/orange mixture; beat ~1½ minutes. Scrape sides. Add remaining mixture in two more additions; beat ~20 seconds after each. If using colour, add and mix until combined.

Divide batter between pans; smooth the tops. Bake ~25‑30 minutes or until a toothpick inserted comes out clean with a few moist crumbs.

Let cakes cool in pans ~10 minutes, then turn out to wire racks to cool completely.

While cakes cool, make frosting: beat butter until creamy; add cream cheese and mix low then medium until smooth. Add vanilla, orange extract, salt; mix. Gradually add powdered sugar and beat until light and fluffy.

Decide if using orange curd. Level cake layers if necessary. Place first layer on plate, spread frosting (and curd if using). Add second layer. Cover top and sides with remaining frosting. Add garnish if desired.

Chill cake ~30–60 minutes, then slice. Bring to room temp ~10 minutes before serving for best flavour.