Prepare the ingredients: Measure and set out all the ingredients before you start.
Make the yeast starter: Dissolve 1 teaspoon honey in½ cup water (warm). Whisk in 1 ½ teaspoon active dry yeast, then ⅔ cup all-purpose flour, until you have a smooth, semi-liquid mixture. Cover the bowl with a clean tea towel or plastic wrap and let it rest in a warm place for 30–45 minutes, until bubbly.
Make the nut filling: In a saucepan, bring 1 ⅓ cups half and half (or milk) to a boil, then remove from heat. Stir in 1 ¼ cups granulated sugar and 5 cups walnuts, ground. Return to very low heat and cook for 3 minutes, stirring constantly. Take off the heat, add 1 teaspoon vanilla paste, 1 Tablespoon lemon zest, and ½ teaspoon cinnamon, then let cool to room temperature.
Make the dough: To a mixing bowl, add 2 ⅔ cups all-purpose flour, ½ cup granulated sugar, ½ cup water, and activated yeast. Mix for 2 minutes, just until combined. Add the salt and softened (or melted, but not hot) 1 stick unsalted butter cut into pieces, ½ teaspoon salt, then knead for 8–10 minutes until the dough is smooth and elastic.
IMPORTANT NOTE: When you add the butter, the dough may look ruined at first – the butter will squelch and resist mixing in. Do not worry, this is normal! Keep the mixer on low with the dough hook, scraping down the sides if needed. Gradually the butter will absorb, and with patient kneading, you will end up with a beautifully soft, elastic dough.
First rise: Cover the bowl with a cloth or plastic wrap and let the dough rise in a warm spot until doubled in size, about 1–2 hours depending on room temperature.
Divide and rest again: Turn the risen dough out onto a lightly floured surface and knead briefly. Divide it into two equal pieces, shape each into a ball, and let them rest for 10 minutes, covered with a cloth.
Roll out the dough: Using a rolling pin, roll one ball of dough into a rectangle about 12 × 10 inches (30 × 25 cm) and ¼ inch (0.5–0.7 cm) thick. Spread half of the cooled walnut filling evenly over the surface, leaving a 1 inch (2.5 cm) border around the edges. An angled cake spatula makes spreading easier.
Shape the roll: Starting from the long side, roll up the dough like a jelly roll, gently tightening as you go. Place the seam on the bottom, tuck the ends under, and set the roll seam side down on a lined baking sheet. Repeat with the second piece of dough.
Egg wash: In a small bowl, beat 1 egg yolk and 1 ½ Tablespoon half and half with a fork. Brush the rolls on all sides with the egg wash.
Second rise: Let the rolls rise for another 30 minutes. For extra shine, brush them once more with the egg wash before baking.
Bake: Preheat the oven to
380 °F, top and bottom heat (no fan). Place the baking sheet on the middle rack and bake for 35 minutes, until golden brown and shiny.