Preheat the oven to 350F (180C). Line an 8 ½ x 4 ½ (21.5 x 11.5 cm) or 9 x 5 inch (33 x 13 cm) loaf pan with parchment paper, or line the bottom and lightly grease the sides.
Ensure the raspberries are completely dry after washing (if using fresh). Toss the raspberries with 1 tablespoon all-purpose flour. Set aside.
In a medium bowl, whisk together the melted butter, vegetable oil, sugar, eggs, lemon juice, vanilla extract and sour cream. Keep whisking until you no longer see pieces of eggs or lumps of sour cream.
In a separate large bowl, whisk together the flour, baking powder, salt and lemon zest. Make a well in the dry ingredients.
Pour the wet ingredients into the well that you made in the dry ingredients. Mix the batter together gently. I typically do a few stirs using a rubber spatula and then whisk with a wire whisk. Do not overmix the batter - otherwise the loaf can become dry and tough.
Gently fold in about 1 cup of the raspberries using a rubber spatula or wooden spoon. Be very careful not to crush the raspberries.
Spoon the batter into the prepared pan, adding in a few raspberries as you go.
Bake in the middle of the preheated oven. Around the 40 minute mark, check the loaf. If the top is already golden brown, then tent a piece of aluminum foil over the top of the pan. The loaf will take about 55-65 minutes if using an 8 ½ x 4 ½ inch pan or about 50-60 minutes if using a 9 x 5 inch pan. If using frozen berries, the loaf will take longer to bake.
Cool the loaf in the pan for at least 30 minutes before gently inverting the loaf and continue cooling on a wire rack.