Preheat the oven to 340°F (170°C).

In a large bowl, beat the eggs with both sugars for 4 to 5 minutes, until the mixture is light and fluffy. With the mixer running, slowly stream in the oil.

Add the sour cream and milk, mixing on low speed until incorporated. Sift the flour, baking powder, and baking soda into the bowl, and mix until just smooth.

Pour the batter into a well-greased pan. Toss the chocolate chips or chunks with 2 tablespoons of flour to prevent them from sinking, then scatter them evenly over the batter. Gently fold them in with a spatula, being careful not to overmix.

Bake for 40 to 45 minutes, or until a toothpick inserted into the center comes out clean. Take care not to overbake; the cake should remain moist.

Allow the cake to cool at room temperature, dust with powdered sugar, and serve.