Heat the oven to 180 C / 356 F. Line a 33 x 23 cm / 13 x 9-inch baking pan with parchment, leaving overhang on two sides to lift the slab out later.

Rub the cold cubed butter into the flour, 100 g sugar, baking powder, and salt with your fingertips until the mixture looks like coarse crumbs.

Add the egg yolks and vanilla extract. Mix with a fork, then knead briefly in the bowl until the dough just comes together and isn't sticky.

Press the dough evenly into the lined pan and prick it all over with a fork.

Bake for 18 to 20 minutes until the edges turn golden brown and the center feels set when lightly pressed.

Cool the crust completely in the pan, about 30 minutes. Spreading jam on a warm crust melts it into a thin, uneven layer, so wait until it's fully cool.

Spread the apricot jam evenly over the cooled crust in a thin, even layer.

Combine the glaze sugar, cocoa powder, milk, and 60 g butter in a 2-quart / 2L saucepan. Whisk over medium heat until the sugar dissolves.

Bring the mixture to a simmer and cook for 2 to 3 minutes, whisking often, until it's glossy and coats the back of a spoon.

Pour the hot glaze over the jam layer and tilt the pan gently so it reaches every edge.

Chill uncovered for 30 minutes until the glaze surface sets, then cover and refrigerate at least 4 hours, or overnight, until fully firm.

Lift the slab out using the parchment overhang. Cut into small squares, about 4 cm / 1.5 inches each, wiping the knife clean between cuts. Serve cold.