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.
*frozen berries combine with 1 tsp flour