How to Make It
Combine milk, cream, brown sugar, vanilla extract, and salt in a large pot. Slowly bring to a gentle simmer over medium-low, stirring occasionally to dissolve sugar. Stir in lemon juice, and gently simmer, undisturbed, until mixture is curdled and whey is clear, about 10 minutes. Remove from heat, and let stand 10 minutes.
Meanwhile, line a large colander with 2 layers of cheesecloth. Carefully pour milk mixture into prepared colander. Place colander over a bowl so that it rests a few inches above bottom of bowl. Chill, uncovered, at least 8 hours or up to 12 hours.
When ready to serve toast, remove colander from bowl, and discard whey in bowl. Squeeze out any remaining excess liquid from ricotta; spoon ricotta into bowl of a stand mixer fitted with the paddle attachment. Beat on medium-high speed just until creamy and smooth, about 15 seconds.
Heat broiler to high. Using a serrated knife, cut cooled kubaneh into quarters. Trim off crust, if desired. Cut bread into 1-inch-thick slices. Lightly butter bread slices on both sides, and place on a baking sheet. Broil on middle rack in preheated oven until toasted, 60 to 90 seconds per side. Spread 1/4 cup brown sugar ricotta on each slice of toast, and top with mixed berries.