Estonian Kringle (Estonia)

Dough

• 30 g sugar
• 1 lemon, thin peelings of skin only (optional)
• 120 g milk
• 30 g unsalted butter, diced
• 15 g fresh yeast, crumbled
  or 1 ½ tsp dried instant yeast
• 1 egg yolk, from medium egg
• 300 g strong white bread flour, plus extra for dusting
• 1 pinch fine sea salt

Filling

• 50 g halved walnuts
  or mixed candied fruit
• 50 g unsalted butter, soft
• 60 g sugar
• 2 Tbsp ground cinnamon

Icing

• 20 g egg whites, lightly beaten
• 50 g icing sugar