Mix room-temperature butter, condensed milk, and salt until well combined.

Add vanilla extract and mix thoroughly.

Sift in the cake flour and combine into a dough.

Separate 50g of the dough and mix it with cocoa powder to form a chocolate dough.

Roll out the white dough flat and place small pieces of cocoa dough on top.

Roll the combined dough to a thickness of 3–4mm using a rolling pin.

Use a cow-shaped cookie cutter to cut out shapes from the dough.

Place the cookies on a baking tray lined with parchment paper or a non-stick sheet.