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Sift together the flour and baking powder and set aside.
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In the bowl of a stand mixer with the whisk attachment in place, whisk together the eggs , sugar and vanilla extract on high speed until foamy and slightly stiffened.
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Mix together the melted butter and vegetable oil in a measuring cup with a spout.
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Slowly add the oil and butter mixture to the egg mixture in a slow stream as the mixer continues to whisk.
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Mix together the whipping cream, milk and lemon juice and add slowly to the mixing bowl continuing to mix but at a reduced speed.
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Fold in the dry ingredients by hand with a rubber spatula being careful not to over mix. Don't worry about a few lumps in the batter, they are fine.
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Pour the batter into a greased and floured 9 inch springform pan or a tube pan. Dot the surface of the batter, a heaping tablespoon at a time with the blueberry jam.
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Using the handle of a wooden spoon, swirl the jam through the batter.