Preheat the Oven

• Preheat your oven to 350°F (175°C).
• Lightly grease a donut pan with nonstick spray or butter.

2. Prepare the Donut Batter

• In a large bowl, whisk together the flour, baking powder, and salt.
• In a separate bowl, mix the melted butter, granulated sugar, and brown sugar until smooth.
• Add the egg, milk, and vanilla extract to the wet ingredients and stir to combine.
• Gradually fold the dry ingredients into the wet mixture until a smooth batter forms.

3. Bake the Donuts

• Transfer the batter to a piping bag for easy filling, or spoon it into the prepared donut pan.
• Fill each cavity about three-quarters full.
• Bake for 10-12 minutes, or until the donuts spring back when lightly touched.
• Allow the donuts to cool in the pan for 5 minutes before transferring them to a wire rack.

4. Make the Custard Filling

• In a saucepan, whisk together egg yolks and sugar until pale and smooth.
• Gradually stir in the heavy cream and vanilla.
• Cook over medium heat, stirring constantly, until the mixture thickens enough to coat the back of a spoon.
• Remove from heat and let cool completely. Transfer to a piping bag fitted with a small nozzle.

5. Fill the Donuts

• Once the donuts are completely cooled, use a small knife or piping tip to create a hole in each donut.
• Pipe the custard filling into the center of each donut.

6. Prepare the Caramel Glaze

• In a small saucepan, combine sugar and water over medium heat. Stir until the sugar dissolves.
• Stop stirring and let the mixture caramelize to a golden brown color.
• Remove from heat and let cool slightly.

7. Glaze the Donuts

• Dip the tops of the filled donuts into the caramel glaze.
• Allow the glaze to set for a few minutes before serving.