High Protein Peanut Butter Swirl Brownies

Preheat the oven to 180°C (160°C fan) / 350°F / Gas Mark 4. Line a 20cm (8-inch) square baking tin with baking parchment.
Melt the butter and chocolate together in a pan over a low heat, or gently in the microwave in short bursts, stirring until smooth. Remove from heat and let it cool slightly.
250 g Butter, 300 g Dark Chocolate
Whisk the eggs and sugars in a large bowl until pale, light, and slightly frothy.
200 g Light Muscovado Sugar, 100 g Dark Muscavado Sugar, 4 Eggs
Fold the chocolate mixture into the egg and sugar mixture until fully combined.
Sift in the plain flour and gently fold it into the batter, taking care not to overmix. The batter should be thick and glossy.
175 g Plain Flour
Add the peanut butter in dollops and swirl it through the batter with a knife or skewer to create a marbled effect. Fold in any optional mix-ins, such as nuts, chocolate chips, or caramel.
250 g Peanut Butter
Pour the batter into the prepared tin, spreading it evenly.
Bake in the preheated oven for 25-30 minutes, or until the edges are set but the centre is slightly underbaked for a fudgy texture. A skewer inserted into the centre should come out with a few moist crumbs.
Cool completely in the tin before slicing into squares. Store in the fridge or freezer for longer keeping; they're also delicious straight from the freezer.