In a small saucepan, melt 63g of unsalted butter over low heat, then set aside.
Add flour, sugar, yeast, salt, nutmeg, and cinnamon to a stand mixing bowl. Whisk dry ingredients together using the paddle attachment until well combined.
Switch the paddle attachment to the dough hook and set your stand mixer to low speed. Begin adding your milk, egg yolks, water and vegetable oil. Mix on medium-low speed until well combined.
Begin slowly introducing the melted butter and mix for an additional 7-10 minutes. Or until almost no dough is sticking to the sides of the mixing bowl.
Loosely roll the dough and place it into a lightly greased bowl. Cover with plastic wrap and a warm damp towel and let stand for 1 hour.
Preheat your oven to 190°C (375°F). Place the sausages onto a tray lined with baking paper, brush over some olive oil and cook the sausages for 30 minutes, turning halfway. Once cooked, remove the sausages from the oven and set them aside to cool.
While still in the bowl, punch down the dough and lightly flour your work surface. Then divide your dough into six even pieces. Roll each piece of dough into ¼” (6-7mm) thick pieces. Then place each sausage at the base and roll, finishing seam side down.
Place onto a baking paper-lined tray, and cover with a warm damp towel to proof for a further 45 minutes at room temperature.
Brush each Kolache with egg wash, then top with flaky salt, sesame, and poppy seeds. Bake in the oven at 190°C (375°F) for 15-18 minutes or until golden brown. Once cooked, brush each Kolache with a little melted butter and let cool before serving.