In a small pot, over medium heat, combine the mixed berries (no need to thaw if they’re frozen) with the sugar, salt, cornstarch and lemon juice.

Stir until the sugar starts to dissolve and then simmer on medium-low heat for 5-10 minutes, until it’s thickened and goes from looking cloudy to more transparent (temp was 210F/99C if you measure).

Press the berry filling through a sieve if you want it seedless and cool completely and refrigerate before assembling the ice cream.

In a medium bowl, heat the butter in the microwave just until it's melted.

Add the brown sugar, flour and cinnamon to the melted butter and use a spoon or a fork to mix it together, until it forms pea-sized chunks. (if the chunks aren't separating, add 1-2 more teaspoons of flour, until they're pea-sized chunks).

Place the heavy whipping cream in the bowl of a stand mixer (or a large bowl with an electric mixer) and beat it at medium speed until it starts to thicken (so it doesn't splash). Increase the speed to high and beat just until it forms stiff peaks.

Add the sweetened condensed milk and salt and beat again just until it's fully combined.

Add half of the chilled berry sauce to the ice cream and half of the streusel. Fold 4-5 times, just until they're swirled into the ice cream and NOT completely combined.

Spread ⅓ of the ice cream into a deep pan and drop globs of the chilled berry sauce on top of the ice cream and use a knife to swirl it back and forth. Then top with a generous amount of streusel.

Repeat with two more layers of ice cream, berry sauce and streusel.

Cover the pan with a lid, plastic wrap or foil and place it in the freezer for at least 8 hours or overnight.