01 - In a small saucepan over low heat, gently melt the butter with the whole milk. Add the granulated sugar and scraped vanilla seeds, stirring continuously until the sugar has fully dissolved and the mixture is smooth.
02 - Remove the saucepan from heat and allow the butter-milk-sugar mixture to cool slightly until lukewarm, then transfer it to a large mixing bowl.
03 - Add the all-purpose flour, baking powder, and fine sea salt to the mixing bowl. Stir with a wooden spoon or spatula until a smooth, homogeneous dough forms and no dry flour pockets remain.
04 - Shape the dough into a ball, wrap it tightly in plastic wrap, and refrigerate for at least 1 hour to firm up the butter and make the dough easier to roll.
05 - Preheat the oven to 350°F (180°C) using conventional bake mode. Line a baking sheet with parchment paper and set aside.
06 - On a lightly floured work surface, roll the chilled dough out to an even thickness of about 1/8 inch (3 to 4 mm), rotating it occasionally to prevent sticking.
07 - Using a traditional fluted rectangular cookie cutter, cut out the petit beurre shapes from the rolled dough. Gather and re-roll scraps as needed to use all the dough.
08 - Place the cut biscuits onto the prepared parchment-lined baking sheet, leaving about 1 inch of space between each one to allow for slight spreading.
09 - Gently prick each biscuit several times with a fork to create the classic dotted pattern. Bake on the middle rack for 12 minutes, or until the edges are golden brown.
10 - Transfer the biscuits to a wire cooling rack immediately and let them cool completely before serving. This ensures they crisp up properly.