Whisk together the all-purpose flour, baking powder, baking soda, and salt in a medium bowl. Set aside.

Add the melted butter, oil, eggs, sugar, sourdough discard, vanilla extract, and buttermilk in a large mixing bowl. Whisk until well combined.

Add the flour mixture to the wet ingredients and fold with a rubber spatula or wooden spoon until almost all are combined.

Add the chopped strawberries and white chocolate chips and fold them through.

The muffins can be baked right away or cold-fermented overnight.

Cold-fermenting - Cover the bowl tightly and place it in the refrigerator for up to 16 hours. Cold fermenting allows the flour to absorb more moisture from the batter, which can lead to a more moist crumb. Additionally, slow fermentation helps break down the proteins in the flour.

Add melted butter, all-purpose flour, sugar, and salt to a small bowl. Use a fork to combine it into a coarse crumb.

As the streusel sits, it will stiffen up and easily crumble with your fingers. Pop it in the fridge for 5 minutes if it's too soft.

Preheat the oven to 425°F (220°C) and grease or line the muffin tin.

Use an ice cream scoop to divide the muffin batter evenly between the lined muffin tin. They will be full.

Generously pile the streusel on top of each muffin. Gently press it on.

Bake for 5 minutes in the preheated oven, then turn the oven down to 350°F (180°C) and bake for 18-20 minutes more until golden brown and the muffin tops spring back when pressed or a cake tester inserted in the middle comes out clean.

Let the baked muffins cool in the pan for 5 minutes before removing them and placing them on a wire rack to cool further.