Step 1: Prepare the Dough

In a large bowl or stand mixer, combine flour, sugar, salt, and instant yeast.

Add eggs and warm milk. Mix until a shaggy dough forms.

Gradually knead in the softened butter, a little at a time, until fully incorporated and the dough is smooth (about 8–10 minutes).

Cover the dough and let it rise in a warm place for 1½ to 2 hours, or until doubled in size.

Step 2: Make the Mascarpone Filling

In a bowl, mix mascarpone, sugar, egg yolk, vanilla extract, and lemon zest (if using) until smooth.

Keep the filling chilled until you’re ready to use it.

Step 3: Roll and Fill the Dough

Once the dough has risen, punch it down and roll it out on a lightly floured surface into a rectangle (about 10×14 inches).

Spread the mascarpone filling evenly over the dough, leaving a small border.

Roll the dough up tightly from the long side into a log.

Slice the log lengthwise down the middle to expose the filling.

Twist the two strands together, ensuring the cut sides face up to reveal the filling.

Step 4: Bake the Babka

Place the twisted loaf in a greased loaf pan. Cover loosely and let it rise again for 30–45 minutes.

Preheat the oven to 180°C (356°F).

Bake for 40–45 minutes, or until the babka is golden and fully cooked through.

Step 5: Cool and Serve

Let the babka cool in the pan for 10 minutes, then transfer it to a wire rack to cool completely.

Dust with powdered sugar if desired and serve warm or at room temperature