Prepare the Butter and Sugar: Beat cold unsalted butter with a mixer on low speed for 1 minute until creamy. Gradually add powdered sugar while mixing on low speed to avoid sugar flying. Increase mixer speed to maximum and beat for 5-8 minutes, stopping every 2 minutes to scrape sides, until the mixture is light, creamy, and pale.
Add Vanilla and Eggs: Add vanilla extract and mix on medium speed. Gradually add room temperature eggs one by one, mixing well after each addition. Scrape sides to ensure even mixing. The dough should remain creamy and smooth.
Add Flour and Salt: Add flour and a pinch of salt. Mix on the lowest speed just until the flour is incorporated and the dough forms. Avoid over-kneading to keep dough soft and tender.
Divide and Flavor Dough: Divide dough into two equal parts. Leave one part as vanilla. To the other half, add unsweetened cocoa powder and softened butter, mixing lightly until evenly colored and combined.
Test Dough Consistency: Take a spoonful of dough and test between hands. It should be soft but not sticky. If sticky, refrigerate dough to cool before shaping.
Shape Petit Fours: Fill a piping bag with dough (do not overfill). Pipe small rose shapes or finger shapes onto an ungreased baking tray, leaving space between each. Keep hands and dough cool to prevent butter from melting. Refrigerate shaped dough trays until ready to bake.
Alternative Shaping with Petit Fours Machine: Chill dough for 15-20 minutes. Press dough through the petit fours machine to form shapes. If shapes are too thick or thin, adjust pressure. Place shapes on tray and refrigerate.
Bake Petit Fours: Preheat oven strongly. Place tray in middle rack. Turn on top grill (broiler) and bake until golden on top. Then switch off top grill and bake at 170°C with bottom heat until golden underneath. Remove once golden on both sides.
Cool and Store: Allow petit fours to cool completely. Store in airtight container with plastic wrap to preserve shape and texture.
Fill and Decorate (Optional): Fill petit fours by sandwiching two pieces with apricot jam or melted chocolate. Press firmly to secure. Dip half in melted chocolate for coating. Optionally decorate with nuts or sprinkles. Let fillings set before serving.