Preheat your oven to 350°F (175°C). Grease a loaf pan with butter or cooking spray to prevent sticking.

In a bowl, whisk together the flour, baking powder, baking soda, and salt until well combined. Set aside.

In a separate large bowl, cream the softened butter and granulated sugar together using an electric mixer until light and fluffy—about 3-5 minutes.

Add the eggs one at a time, beating well after each addition. Then stir in the lemon zest, lemon juice, and vanilla extract, mixing well.

Gradually add the dry ingredients to the wet ingredients, mixing until just combined. It’s important not to overmix the batter; a few lumps are perfectly fine!

Carefully fold in the chopped rhubarb and walnuts (if using) into the batter, ensuring an even distribution.

Pour the batter into your prepared loaf pan, smoothing the top. Bake in the preheated oven for 60-75 minutes, or until the top is golden and a toothpick inserted into the center comes out clean.

Allow the bread to cool in the pan for 10 minutes before transferring it to a wire rack to cool completely.