Preheat oven to 180 C temp.

In a big bowl, using an electric mixer, beat butter, mascarpone, sugar, vanilla extract, lemon zest, juice until smooth and creamy.

Add eggs one at a time and lightly whisk just until incorporated.

In another bowl, combine flour, baking powder, salt. Add into the wet ingredients bowl. Mix with a spatula until just combined.

Add berries and gently combine into a dough.

Line loaf pan (25x11 cm) with a parchment paper. Pour dough into a pan. 

Bake about 50-55 min.